refactor(sources/cloudsqladmin): move source implementation in Invoke() function to Source (#2233)

Move source-related queries from `Invoke()` function into Source.

This is an effort to generalizing tools to work with any Source that
implements a specific interface. This will provide a better segregation
of the roles for Tools vs Source.

Tool's role will be limited to the following:
* Resolve any pre-implementation steps or parameters (e.g. template
parameters)
* Retrieving Source
* Calling the source's implementation


Along with these updates, this PR also resolve some comments from
Gemini:
* update `fmt.Printf()` to logging as a Debug log and remove the
training `\n` within the log
* move `regexp.MustCompile` to the top so that it's compiled once at the
package level and reused. It is a relatively expensive operation to be
called on every invocation.
* `fetchInstanceData()` to return the `*sqladmin.DatabaseInstance`
struct directly instead of converting to map and use map lookups. More
typesafe and efficient.


Did not move `cloudsqlpgupgradeprecheck` tool since that invocation is
very specific towards cloudsql for postgres

internal/tools/cloudsqlmysql/cloudsqlmysqlcreateinstance/cloudsqlmysqlcreateinstance.go

@@ -44,8 +44,8 @@ func newConfig(ctx context.Context, name string, decoder *yaml.Decoder) (tools.T
 
 type compatibleSource interface {
 	GetDefaultProject() string
-	GetService(context.Context, string) (*sqladmin.Service, error)
 	UseClientAuthorization() bool
+	CreateInstance(context.Context, string, string, string, string, sqladmin.Settings, string) (any, error)
 }
 
 // Config defines the configuration for the create-instances tool.
@@ -167,25 +167,7 @@ func (t Tool) Invoke(ctx context.Context, resourceMgr tools.SourceProvider, para
 		return nil, fmt.Errorf("invalid 'editionPreset': %q. Must be either 'Production' or 'Development'", editionPreset)
 	}
 
-	instance := sqladmin.DatabaseInstance{
-		Name:            name,
-		DatabaseVersion: dbVersion,
-		RootPassword:    rootPassword,
-		Settings:        &settings,
-		Project:         project,
-	}
-
-	service, err := source.GetService(ctx, string(accessToken))
-	if err != nil {
-		return nil, err
-	}
-
-	resp, err := service.Instances.Insert(project, &instance).Do()
-	if err != nil {
-		return nil, fmt.Errorf("error creating instance: %w", err)
-	}
-
-	return resp, nil
+	return source.CreateInstance(ctx, project, name, dbVersion, rootPassword, settings, string(accessToken))
 }
 
 // ParseParams parses the parameters for the tool.