Login with OIDC

[jschwanz]

Checklist

• [X] All new jobs, commands, executors, parameters have descriptions
• [X] Examples have been added for any significant new features
• [X] README has been updated, if necessary

Motivation, issues

Both CircleCI and Azure support OIDC, so it makes sense that the orb support this method of authentication.

Description

Add login-with-oidc command.