feat: Add Bigtable source and tool (#418)

# Add Bigtable support

A `bigtable` source can be added as the following example

```
sources:
  test-bigtable-source:
    kind: "bigtable"
    project: "sample-project"
    instance: "sample-instance"
```

A `bigtable` tool can be added as below

```
tools:
  get-test-tool-data:
    kind: bigtable-sql
    source: test-bigtable-source
    description: Some description
    statement: SELECT * FROM `test-table` WHERE address['state'] = @state;
    parameters:
      - name: state
        type: string
        description: Filter by state
```

---------

Co-authored-by: Yuan <45984206+Yuan325@users.noreply.github.com>
Co-authored-by: Kurtis Van Gent <31518063+kurtisvg@users.noreply.github.com>
Co-authored-by: Wenxin Du <117315983+duwenxin99@users.noreply.github.com>

.golangci.yaml

@@ -45,3 +45,4 @@ run:
     - mysql
     - http
     - alloydb_ai_nl
+    - bigtable