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Existing tools.yaml configuration files are now in an outdated format.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pre-processing layer that automatically detects outdated configuration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.go

@@ -25,11 +25,11 @@ import (
 	"github.com/googleapis/genai-toolbox/internal/util/parameters"
 )
 
-const kind string = "cloud-sql-create-users"
+const resourceType string = "cloud-sql-create-users"
 
 func init() {
-	if !tools.Register(kind, newConfig) {
-		panic(fmt.Sprintf("tool kind %q already registered", kind))
+	if !tools.Register(resourceType, newConfig) {
+		panic(fmt.Sprintf("tool type %q already registered", resourceType))
 	}
 }
 
@@ -50,7 +50,7 @@ type compatibleSource interface {
 // Config defines the configuration for the create-user tool.
 type Config struct {
 	Name         string   `yaml:"name" validate:"required"`
-	Kind         string   `yaml:"kind" validate:"required"`
+	Type         string   `yaml:"type" validate:"required"`
 	Source       string   `yaml:"source" validate:"required"`
 	Description  string   `yaml:"description"`
 	AuthRequired []string `yaml:"authRequired"`
@@ -59,9 +59,9 @@ type Config struct {
 // validate interface
 var _ tools.ToolConfig = Config{}
 
-// ToolConfigKind returns the kind of the tool.
-func (cfg Config) ToolConfigKind() string {
-	return kind
+// ToolConfigType returns the type of the tool.
+func (cfg Config) ToolConfigType() string {
+	return resourceType
 }
 
 // Initialize initializes the tool from the configuration.
@@ -72,7 +72,7 @@ func (cfg Config) Initialize(srcs map[string]sources.Source) (tools.Tool, error)
 	}
 	s, ok := rawS.(compatibleSource)
 	if !ok {
-		return nil, fmt.Errorf("invalid source for %q tool: source kind must be `cloud-sql-admin`", kind)
+		return nil, fmt.Errorf("invalid source for %q tool: source type must be `cloud-sql-admin`", resourceType)
 	}
 
 	project := s.GetDefaultProject()
@@ -120,7 +120,7 @@ func (t Tool) ToConfig() tools.ToolConfig {
 
 // Invoke executes the tool's logic.
 func (t Tool) Invoke(ctx context.Context, resourceMgr tools.SourceProvider, params parameters.ParamValues, accessToken tools.AccessToken) (any, error) {
-	source, err := tools.GetCompatibleSource[compatibleSource](resourceMgr, t.Source, t.Name, t.Kind)
+	source, err := tools.GetCompatibleSource[compatibleSource](resourceMgr, t.Source, t.Name, t.Type)
 	if err != nil {
 		return nil, err
 	}
@@ -170,7 +170,7 @@ func (t Tool) Authorized(verifiedAuthServices []string) bool {
 }
 
 func (t Tool) RequiresClientAuthorization(resourceMgr tools.SourceProvider) (bool, error) {
-	source, err := tools.GetCompatibleSource[compatibleSource](resourceMgr, t.Source, t.Name, t.Kind)
+	source, err := tools.GetCompatibleSource[compatibleSource](resourceMgr, t.Source, t.Name, t.Type)
 	if err != nil {
 		return false, err
 	}