Improve entity fetching from db

[franticticktick]

It is necessary to improve the way of fetching entities from the database in accordance with the pattern suggested by @jzheaux , using the example of JdbcPublicKeyCredentialUserEntityRepository:

		if (existsUserEntity) {
			updateUserEntity(userEntity);
		}
		else {
			try {
				insertUserEntity(userEntity);
			}
			catch (DuplicateKeyException ex) {
				updateUserEntity(userEntity);
			}
		}

Thic code can be replaced by:

		int rows = updateUserEntity(userEntity);
		if (rows == 0) {
			insertUserEntity(userEntity);
		}

This polish can be done in the following components:

• JdbcOAuth2AuthorizedClientService method saveAuthorizedClient
• JdbcUserCredentialRepository method save

If possible, tests should be left as is.

[jzheaux]

Thanks, @franticticktick. I'll close this in favor of #16727