Auth: Add Sigv4 auth option to datasources (#27552)

* create transport chain

* add frontend

* remove log

* inline field updates

* allow ARN, Credentials + Keys auth in frontend

* configure credentials

* add tests and refactor

* update frontend json field names

* fix tests

* fix comment

* add app config flag

* refactor tests

* add return field for tests

* add flag for UI display

* update comment

* move logic

* fix config

* pass config through props

* update docs

* pr feedback and add docs coverage

* shorten settings filename

* fix imports

* revert docs changes

* remove log line

* wrap up next as round tripper

* only propagate required config

* remove unused import

* remove ARN option and replace with default chain

* make ARN role assume as supplemental

* update docs

* refactor flow

* sign body when necessary

* remove unnecessary wrapper

* remove newline

* Apply suggestions from code review

* PR fixes

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

pkg/api/frontendsettings.go

@@ -203,6 +203,7 @@ func (hs *HTTPServer) getFrontendSettingsMap(c *models.ReqContext) (map[string]i
 		"alertingMinInterval":        setting.AlertingMinInterval,
 		"autoAssignOrg":              setting.AutoAssignOrg,
 		"verifyEmailEnabled":         setting.VerifyEmailEnabled,
+		"sigV4AuthEnabled":           setting.SigV4AuthEnabled,
 		"exploreEnabled":             setting.ExploreEnabled,
 		"googleAnalyticsId":          setting.GoogleAnalyticsId,
 		"disableLoginForm":           setting.DisableLoginForm,