Improve error codes for user defined local authenticator management.

[Thisara-Welmilla]

Task issue:

• Provide API for the new custom authentication management #21216

Fix having duplicated error code for following scenrio which related to user defined local authenticators.

1. Having same error code for authenticator name valdiation and the blank display name.
2. Having same error code, but differnet error messages for the invalid endpoint confgiuration scenrios.

[Thisara-Welmilla]

PRs:

• Improve error codes for user defined local authenticator mgt. carbon-identity-framework#6212
• Improve error codes for user defined local authenticator mgt identity-api-server#760
• Improve error codes for user defined local authenticator mgt. carbon-identity-framework#6233