feat!: update configuration file v2 (#2369)

This PR introduces a significant update to the Toolbox configuration
file format, which is one of the primary **breaking changes** required
for the implementation of the Advanced Control Plane.

# Summary of Changes
The configuration schema has been updated to enforce resource isolation
and facilitate atomic, incremental updates.
* Resource Isolation: Resource definitions are now separated into
individual blocks, using a distinct structure for each resource type
(Source, Tool, Toolset, etc.). This improves readability, management,
and auditing of configuration files.
* Field Name Modification: Internal field names have been modified to
align with declarative methodologies. Specifically, the configuration
now separates kind (general resource type, e.g., Source) from type
(specific implementation, e.g., Postgres).

# User Impact
Existing tools.yaml configuration files are now in an outdated format.
Users must eventually update their files to the new YAML format.

# Mitigation & Compatibility
Backward compatibility is maintained during this transition to ensure no
immediate user action is required for existing files.
* Immediate Backward Compatibility: The source code includes a
pre-processing layer that automatically detects outdated configuration
files (v1 format) and converts them to the new v2 format under the hood.
* [COMING SOON] Migration Support: The new toolbox migrate subcommand
will be introduced to allow users to automatically convert their old
configuration files to the latest format.

# Example
Example for config file v2:
```
kind: sources
name: my-pg-instance
type: cloud-sql-postgres
project: my-project
region: my-region
instance: my-instance
database: my_db
user: my_user
password: my_pass
---
kind: authServices
name: my-google-auth
type: google
clientId: testing-id
---
kind: tools
name: example_tool
type: postgres-sql
source: my-pg-instance
description: some description
statement: SELECT * FROM SQL_STATEMENT;
parameters:
- name: country
  type: string
  description: some description
---
kind: tools
name: example_tool_2
type: postgres-sql
source: my-pg-instance
description: returning the number one
statement: SELECT 1;
---
kind: toolsets
name: example_toolset
tools:
- example_tool
```

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Averi Kitsch <akitsch@google.com>

internal/tools/cloudsql/cloudsqlcreateusers/cloudsqlcreateusers_test.go

@@ -17,7 +17,6 @@ package cloudsqlcreateusers_test
 import (
 	"testing"
 
-	"github.com/goccy/go-yaml"
 	"github.com/google/go-cmp/cmp"
 	"github.com/googleapis/genai-toolbox/internal/server"
 	"github.com/googleapis/genai-toolbox/internal/testutils"
@@ -37,16 +36,16 @@ func TestParseFromYaml(t *testing.T) {
 		{
 			desc: "basic example",
 			in: `
-			tools:
-				create-user:
-					kind: cloud-sql-create-users
-					source: my-source
-					description: some description
+			kind: tools
+			name: create-user
+			type: cloud-sql-create-users
+			source: my-source
+			description: some description
 			`,
 			want: server.ToolConfigs{
 				"create-user": cloudsqlcreateusers.Config{
 					Name:         "create-user",
-					Kind:         "cloud-sql-create-users",
+					Type:         "cloud-sql-create-users",
 					Source:       "my-source",
 					Description:  "some description",
 					AuthRequired: []string{},
@@ -56,15 +55,11 @@ func TestParseFromYaml(t *testing.T) {
 	}
 	for _, tc := range tcs {
 		t.Run(tc.desc, func(t *testing.T) {
-			got := struct {
-				Tools server.ToolConfigs `yaml:"tools"`
-			}{}
-			// Parse contents
-			err := yaml.UnmarshalContext(ctx, testutils.FormatYaml(tc.in), &got)
+			_, _, _, got, _, _, err := server.UnmarshalResourceConfig(ctx, testutils.FormatYaml(tc.in))
 			if err != nil {
 				t.Fatalf("unable to unmarshal: %s", err)
 			}
-			if diff := cmp.Diff(tc.want, got.Tools); diff != "" {
+			if diff := cmp.Diff(tc.want, got); diff != "" {
 				t.Fatalf("incorrect parse: diff %v", diff)
 			}
 		})