Support OAuth Token for Kubernetes Authentication via Credential Service

[minwoox]

Motivation: The current approach stores the Kubernetes oauthToken in the Kubernetes configuration, which is not ideal for sensitive information. To improve security, we need a way to specify and manage the oauthToken through the credential service, allowing it to be securely retrieved and used by the Kubernetes service.

Modifications:

• Added functionality to use the oauthToken for Kubernetes authentication via the credential service if the token is specified with credential:.

Result:

• Kubernetes OAuth tokens can now be securely managed and retrieved through the credential service.

[jrhee17]

Let me wait until this is rebased over https://github.com/line/centraldogma/pull/1031 since it is difficult to review the changes related to OAuth Token.

[minwoox]

Let me wait until this is rebased over https://github.com/line/centraldogma/pull/1031 since it is difficult to review the changes related to OAuth Token.

Yeah, let me ping you when it's ready. 😉

[minwoox]

@jrhee17, @ikhoon this is now ready. 😉