OAuth: Add optional strict parsing of role_attribute_path (#28021)

* OAuth: Add strict role mapping

By default the user is assigned the role Viewer if role_attribute_path
doesn't return a role, which is not always desirable. This commit adds a
strict mode, which deny the user access if a role isn't returned.

Fix #26626

* Update docs/sources/auth/generic-oauth.md

Co-authored-by: Emil Tullstedt <emil.tullstedt@grafana.com>

* Update docs/sources/auth/generic-oauth.md

* Update .gitignore file with WAN

* Removed WAN from .gitignore

Co-authored-by: Emil Tullstedt <emil.tullstedt@grafana.com>
Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>
Co-authored-by: achatterjee-grafana <aparajita.chatterjee@grafana.com>

pkg/setting/setting_oauth.go

@@ -8,6 +8,7 @@ type OAuthInfo struct {
 	EmailAttributeName     string
 	EmailAttributePath     string
 	RoleAttributePath      string
+	RoleAttributeStrict    bool
 	AllowedDomains         []string
 	HostedDomain           string
 	ApiUrl                 string