Need to support OAUTH for bitbucket

### What feature do you want to see added?

Add native support for Bitbucket Cloud OAuth 2.0 authentication within the Git plugin.

Currently, authentication primarily relies on SSH keys, usernames/passwords, app passwords, or personal access tokens. As Bitbucket Cloud continues to encourage OAuth-based authentication and organizations move away from long-lived credentials, the Git plugin should support OAuth 2.0 as a first-class authentication method.

The implementation should ideally:

* Add a Bitbucket Cloud OAuth 2.0 credential type that integrates with the Jenkins Credentials system.
* Support OAuth authorization and automatic access token refresh using refresh tokens.
* Allow OAuth credentials to be selected anywhere Git credentials are currently used (freestyle jobs, Pipeline, Multibranch Pipeline, etc.).
* Eliminate the need to manage static credentials for Git operations against Bitbucket Cloud.
* Improve security by leveraging short-lived access tokens instead of long-lived credentials.

This would provide a more secure and modern authentication experience while aligning with Bitbucket Cloud's recommended authentication methods.

### Upstream changes

None.

### Are you interested in contributing this feature?

Yes. I would be interested in helping test the implementation and provide feedback. I may also be able to contribute code if guidance is provided on the preferred implementation approach.

Start by tracing how the Git plugin integrates with the Jenkins Credentials system and how credentials are selected for freestyle jobs, Pipeline, and Multibranch Pipeline. Define the Bitbucket Cloud OAuth 2.0 credential flow, including authorization and refresh-token handling. Done means OAuth credentials work anywhere existing Git credentials are accepted without static credentials.

Written by the indexing model from the issue text.