Support scoped access tokens (#20908)

This PR adds the support for scopes of access tokens, mimicking the
design of GitHub OAuth scopes.

The changes of the core logic are in `models/auth` that `AccessToken`
struct will have a `Scope` field. The normalized (no duplication of
scope), comma-separated scope string will be stored in `access_token`
table in the database.
In `services/auth`, the scope will be stored in context, which will be
used by `reqToken` middleware in API calls. Only OAuth2 tokens will have
granular token scopes, while others like BasicAuth will default to scope
`all`.
A large amount of work happens in `routers/api/v1/api.go` and the
corresponding `tests/integration` tests, that is adding necessary scopes
to each of the API calls as they fit.


- [x] Add `Scope` field to `AccessToken`
- [x] Add access control to all API endpoints
- [x] Update frontend & backend for when creating tokens
- [x] Add a database migration for `scope` column (enable 'all' access
to past tokens)

I'm aiming to complete it before Gitea 1.19 release.

Fixes #4300

models/migrations/migrations.go

@@ -451,6 +451,8 @@ var migrations = []Migration{
 	NewMigration("Drop ForeignReference table", v1_19.DropForeignReferenceTable),
 	// v238 -> v239
 	NewMigration("Add updated unix to LFSMetaObject", v1_19.AddUpdatedUnixToLFSMetaObject),
+	// v239 -> v240
+	NewMigration("Add scope for access_token", v1_19.AddScopeForAccessTokens),
 }
 
 // GetCurrentDBVersion returns the current db version