Auth: Extended JWT client for OBO and Service Authentication (#83814)

* reenable ext-jwt-client

* fixup settings struct

* add user and service auth

* lint up

* add user auth to grafana ext

* fixes

* Populate token permissions

Co-authored-by: jguer <joao.guerreiro@grafana.com>

* fix tests

* fix lint

* small prealloc

* small prealloc

* use special namespace for access policies

* fix access policy auth

* fix tests

* fix uncalled settings expander

* add feature toggle

* small feedback fixes

* rename entitlements to permissions

* add authlibn

* allow viewing the signed in user info for non user namespace

* fix invalid namespacedID

* use authlib as verifier for tokens

* Update pkg/services/authn/clients/ext_jwt.go

Co-authored-by: Gabriel MABILLE <gamab@users.noreply.github.com>

* Update pkg/services/authn/clients/ext_jwt_test.go

Co-authored-by: Gabriel MABILLE <gamab@users.noreply.github.com>

* fix parameter names

* change asserts to normal package

* add rule for assert

* fix ownerships

* Local diff

* test and lint

* Fix test

* Fix ac test

* Fix pluginproxy test

* Revert testdata changes

* Force revert on test data

---------

Co-authored-by: gamab <gabriel.mabille@grafana.com>
Co-authored-by: Gabriel MABILLE <gamab@users.noreply.github.com>

pkg/services/auth/identity/requester.go

@@ -14,6 +14,7 @@ const (
 	NamespaceServiceAccount = "service-account"
 	NamespaceAnonymous      = "anonymous"
 	NamespaceRenderService  = "render"
+	NamespaceAccessPolicy   = "access-policy"
 )
 
 var ErrNotIntIdentifier = errors.New("identifier is not an int64")