feat(oidc): add configurable login auto-redirect

[ajgon]

Summary

A little improvement, which allows to skip "Login with OIDC" panel altogether, and redirect user directly to login page. This is useful when multiple applications are hidden behind the same OIDC provider, and logging in to one of them, authenticates session everywhere. With this change, the user will be automatically redirected to /oidc/login page, and since they're logged in - automatically signed in and get back to gatus panel. Which saves a one click :-)

I also made this behavior configurable, via security.oidc.login-redirect option, which is set to false by default, to maintain current approach.

P.S. My Vue skills are pretty non-existent, so I'm not sure if it's the best approach to do this on static website side. If there is better, I'm happy to adjust it if necessary.

Checklist

• Tested and/or added tests to validate that the changes work as intended, if applicable.
• Updated documentation in README.md, if applicable.