Internationalize login page

Krishna on the Globalization QE team pointed out that the login page is not internationalized. We should find a solution here.

The login page is not part of the console repo. It is part of the OAuth server and doesn't use react. The simple solution would be to make the labels for the username and password inputs parameters in the Go template and fill in the correct values based on the Accept-Language header.

Most likely we won't be able to use the language user preference since the user hasn't logged yet and user preferences are tied to a specific user ID.

Additional info:

Most of the pieces are already in place, meaning that all the templates are already using the GO templates syntax.

Following tasks will need to be done:

• read the proper Accept-Language header in the oauth-server, and based on the language parse the template
• extend default and custom templates with the i18n Go template syntax
• figure out where the localised strings should be placed - easiest way would be to put them directly to oauth-server repo since otherwise we would need to vendor them.
• come up with the edge case scenarios (eg. what happens if the header contains unsupported language, …)