feat: manage bot accounts from the admin UI, API and CLI (#38966)

Adds first-class bot accounts (`UserTypeBot`): local, password-less
users for automation that authenticate only with access tokens.

1. Admin UI: create bots, filter users by type, manage a bot's access
tokens, convert between user and bot
2. API: `POST /admin/users/{username}/convert-type`, and user objects
gain a GitHub-compatible `type` (`User`, `Organization`, `Bot`)
3. CLI: `gitea admin user change-type`, `--user-type` accepts `User` or
`Bot` case-insensitively
4. Converting keeps the password, 2FA, OAuth2 grants and access tokens,
and since sign-in rejects bots, converting back restores the account.
Only local, non-admin accounts can be converted, and conversions are
audited
5. Session, reverse proxy, SSPI, external source and password reset
sign-in reject non-individual users, so a bot never gets an interactive
session
6. Bots receive no notifications or emails

Co-authored-by: Nicolas <bircni@icloud.com>
Co-authored-by: joestump <joe@joestump.net>
Co-authored-by: Joe Stump <joe@stu.mp>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

routers/api/v1/api.go

@@ -1905,6 +1905,7 @@ func Routes() *web.Router {
 					m.Post("/orgs", bind(api.CreateOrgOption{}), admin.CreateOrg)
 					m.Post("/repos", bind(api.CreateRepoOption{}), admin.CreateRepo)
 					m.Post("/rename", bind(api.RenameUserOption{}), admin.RenameUser)
+					m.Post("/convert-type", bind(api.ConvertUserTypeOption{}), admin.ConvertUserType)
 					m.Get("/badges", admin.ListUserBadges)
 					m.Post("/badges", bind(api.UserBadgeOption{}), admin.AddUserBadges)
 					m.Delete("/badges", bind(api.UserBadgeOption{}), admin.DeleteUserBadges)