Add Passkey login support

[anbraten]

closes #22015

After adding a passkey, you can now simply login with it directly by clicking Sign in with a passkey.

Note for testing. You need to run gitea using https to get the full passkeys experience.

[silverwind]

Unrelated, but I see we need to increase contrast on these error message headers :)

[silverwind]

Looks alright, but I have not tested it.

[lunny]

Thank you for your contributions. But I don't think the login UI is ideal. Maybe we can have a redesign because of Passkey login supported?

[anbraten]

Thank you for your contributions. But I don't think the login UI is ideal. Maybe we can have a redesign because of Passkey login supported?

Sure, I am open for suggestions.

Using a link seemedd nice as it isn't to dominated compared to another button as not every system is supporting passkeys yet. Mainly orientated on Githubs approach (which seems pretty clean):

[silverwind]

I think we could do the same and separate the links into a separate box. Moving the "Forget Password" besides the password label is also a good idea to make it look less crammed.

I can help on these parts if you like.

[anbraten]

That sounds great. Feel free to push to this PR.

[silverwind]

I will. Another change I plan is to make the "Sign In" button full width. It'll look better, be easier to click and match the OAuth buttons as well.

[anbraten]

@silverwind Did some testing: