feat: add restriction mode

[tobiasehlert]

Add environmental flag to enable/disable "restriction mode" and some logic around that.
This to prevent flooding of upstream website that can cause subsequent issues, so limiting endpoints should be possible by this.
Highscores endpoint is subject to this restriction as of now, to only be allowed vocation all to be accessible when enabled.

When restriction-mode is enabled, the only valid vocation enum on highscores should be all.
When restriction-mode is disabled (default behaviour), filtering is supported as normal.

This is requested through dialog with Cipsoft.