feat: Added Neo4j Source and Tool (#189)

- configure neo4j source with url, username, password, database
- configure neo4j tools with cypher statement and paramters
- tests based on the postgres tests
- neo4j.yaml for integration tests
---------

Co-authored-by: duwenxin <duwenxin@google.com>

docs/sources/README.md

@@ -30,3 +30,4 @@ We currently support the following types of kinds of sources:
   PostgreSQL instance.
 * [postgres](./postgres.md) - Connect to any PostgreSQL compatible database.
 * [spanner](./spanner.md) - Connect to a Spanner database.
+* [neo4j](./neo4j.md) - Connect to a Neo4j instance.

docs/sources/neo4j.md

@@ -0,0 +1,40 @@
+# Neo4j Source 
+
+[Neo4j][neo4j-docs] is a powerful, open source graph database
+system with over 15 years of active development that has earned it a strong
+reputation for reliability, feature robustness, and performance.
+
+[neo4j-docs]: https://neo4j.com/docs
+
+## Requirements 
+
+### Database User
+
+This source only uses standard authentication. You will need to [create a
+Neo4j user][neo4j-users] to log in to the database with, or use the default `neo4j` user if available. 
+
+[neo4j-users]: https://neo4j.com/docs/operations-manual/current/authentication-authorization/manage-users/
+
+## Example
+
+```yaml
+sources:
+    my-neo4j-source:
+        kind: "neo4j"
+        uri: "neo4j+s://xxxx.databases.neo4j.io:7687"
+        user: "neo4j"
+        password: "my-password"
+        database: "neo4j"
+```
+
+## Reference
+
+| **field** | **type** | **required** | **description**                                                     |
+|-----------|:--------:|:------------:|---------------------------------------------------------------------|
+| kind      |  string  |     true     | Must be "neo4j".                                                    |
+| uri       |  string  |     true     | Connect URI ("bolt://localhost", "neo4j+s://xxx.databases.neo4j.io") |
+| user      |  string  |     true     | Name of the Neo4j user to connect as (e.g. "neo4j").                |
+| password  |  string  |     true     | Password of the Neo4j user (e.g. "my-password").                    |
+| database  |  string  |     true     | Name of the Neo4j database to connect to (e.g. "neo4j").            |
+
+

docs/tools/README.md

@@ -50,6 +50,9 @@ We currently support the following types of kinds of tools:
   PostgreSQL-compatible database.
 * [spanner](./spanner.md) - Run a Spanner (either googlesql or postgresql)
   statement againts Spanner database.
+* [neo4j-cypher](./neo4j-cypher.md) - Run a Cypher statement against a
+  Neo4j database.
+
 
 ## Specifying Parameters
 

docs/tools/neo4j-cypher.md

@@ -0,0 +1,59 @@
+# Neo4j Cypher Tool 
+
+A "neo4j-cypher" tool executes a pre-defined Cypher statement against a Neo4j database. It's compatible with any of the following sources:
+- [neo4j](../sources/neo4j.md)
+
+The specified Cypher statement is executed as a [parameterized statement][neo4j-parameters],
+and specified parameters will be used according to their name: e.g. `$id`.
+
+[neo4j-parameters]: https://neo4j.com/docs/cypher-manual/current/syntax/parameters/
+
+## Example
+
+```yaml
+tools:
+ search_movies_by_actor:
+    kind: neo4j-cypher
+    source: my-neo4j-movies-instance
+    statement: |
+      MATCH (m:Movie)<-[:ACTED_IN]-(p:Person)
+      WHERE p.name = $name AND m.year > $year
+      RETURN m.title, m.year
+      LIMIT 10
+    description: |
+      Use this tool to get a list of movies for a specific actor and a given minium release year.
+      Takes an full actor name, e.g. "Tom Hanks" and a year e.g 1993 and returns a list of movie titles and release years.
+      Do NOT use this tool with a movie title. Do NOT guess an actor name, Do NOT guess a year.
+      A actor name is a fully qualified name with first and last name separated by a space.
+      For example, if given "Hanks, Tom" the actor name is "Tom Hanks".
+      If the tool returns more than one option choose the most recent movies.
+      Example:
+      {{
+          "name": "Meg Ryan",
+          "year": 1993
+      }}
+      Example:
+      {{
+          "name": "Clint Eastwood",
+          "year": 2000
+      }}
+    parameters:
+      - name: name
+        type: string
+        description: Full actor name, "firstname lastname"
+      - name: year
+        type: integer
+        description: 4 digit number starting in 1900 up to the current year 
+```
+
+## Reference
+
+| **field**   |  **type** | **required** | **description**                                                                                    |
+|-------------|----------:|:------------:|----------------------------------------------------------------------------------------------------|
+| kind        |    string |     true     | Must be "neo4j-cypher".                                                                            |
+| source      |    string |     true     | Name of the source the Cypher query should execute on.                                             |
+| description |    string |     true     | Description of the tool                                                                            |
+| statement   |    string |     true     | Cypher statement to execute                                                                        |
+| parameters  | parameter |     true     | List of [parameters](README.md#specifying-parameters) that will be used with the Cypher statement. |
+
+