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

tests/integration/api_user_follow_test.go

@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"testing"
 
+	auth_model "code.gitea.io/gitea/models/auth"
 	api "code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/tests"
 
@@ -24,7 +25,7 @@ func TestAPIFollow(t *testing.T) {
 	token1 := getTokenForLoggedInUser(t, session1)
 
 	session2 := loginUser(t, user2)
-	token2 := getTokenForLoggedInUser(t, session2)
+	token2 := getTokenForLoggedInUser(t, session2, auth_model.AccessTokenScopeUserFollow)
 
 	t.Run("Follow", func(t *testing.T) {
 		defer tests.PrintCurrentTest(t)()