fix: JENKINS-69414 - Add OAuth 2.0 support

[slide]

This adds a checkbox to the mail account configuration to allow users to enable OAuth 2.0 (see https://javaee.github.io/javamail/OAuth2).

The token needs to be put as the password in the credentials.

See https://issues.jenkins.io/browse/JENKINS-69414

I tested with Gmail using my email address and the OAuth 2.0 token as the password in the credential for the MailAccount.

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[slide]

Is this repo participating in Hacktoberfest? If so, can this be labelled as such?

[basil]

Released in 2.92.