Open up account registrations to the public

This issue tracks requirements for what we need in order to feel confident to open Keycloak (and therefore GitLab up to the public).

• User registration security audit
• Sensible password restrictions
• Recaptcha for user registration (#35 (closed))
• Login flow audit
• GitLab security audit
• Keycloak monitoring (#23)
• GitLab monitoring (#14)
• Review secure Gitlab runner (#74 (closed))
• GitLab secure runner for our own projects with proper restrictions (#32 (closed))
• Audit security of public runners (#8 (closed))
• Add github.com as identity provider (#2 (closed))
• Add gitlab.com as identity provider (#40 (closed))
• Allow incoming mail on GitLab (#3 (closed))
• Enable Keycloak event logging (#68 (closed))
• Finish Arch theme of Keycloak (!28 (merged))
• Research fine grade permissions for externals (#9 (closed))
• Fix GitLab backups (#118 (closed))
• Validate GitLab backups
• Validate Keycloak backups