feat: implement AddZitadelProvider in ManagementService (#12056)

# Which Problems Are Solved

This PR adds implementation to add a Zitadel IdP at the
organization-level.

# How the Problems Are Solved
- Added handling/converters for the `AddZitadelProvider` endpoint in
`ManagementService` in the server layer
- Registered a new `org.idp.zitadel.added` event for org-level Zitadel
providers
- Added `AddOrgZitadelProvider` command to validate the request and push
`org.idp.zitadel.added` event to the eventstore
- Added the `org.idp.zitadel.added` event to the projection reducer
- Added unit and integration tests

# Additional Changes
added more tests for the ZitadelProvider in AdminService

# Additional Context
- Closes https://github.com/zitadel/zitadel/issues/11823
- Follow-up for PRs https://github.com/zitadel/zitadel/pull/12018,
https://github.com/zitadel/zitadel/pull/12020,
https://github.com/zitadel/zitadel/pull/12055

internal/command/instance_idp.go

@@ -1946,7 +1946,7 @@ func (c *Commands) AddInstanceZitadelProvider(ctx context.Context, provider Zita
 		return "", nil, err
 	}
 
-	err = c.validateZitadelProvider(ctx, &provider)
+	err = c.validateInstanceZitadelProvider(&provider)
 	if err != nil {
 		return "", nil, err
 	}
@@ -1996,7 +1996,7 @@ func (c *Commands) prepareAddInstanceZitadelProvider(a *instance.Aggregate, writ
 	}
 }
 
-func (c *Commands) validateZitadelProvider(ctx context.Context, provider *ZitadelProvider) error {
+func (c *Commands) validateInstanceZitadelProvider(provider *ZitadelProvider) error {
 	if provider.Name = strings.TrimSpace(provider.Name); provider.Name == "" {
 		return zerrors.ThrowInvalidArgument(nil, "INST-Sgtj5", "Errors.Invalid.Argument")
 	}