[main] Plugin fixes (#57399)

* Plugins: Remove support for V1 manifests

* Plugins: Make proxy endpoints not leak sensitive HTTP headers

* Security: Fix do not forward login cookie in outgoing requests

(cherry picked from commit 4539c33fce)

Co-authored-by: Will Browne <wbrowne@users.noreply.github.com>

pkg/api/datasources.go

@@ -827,7 +827,7 @@ func (hs *HTTPServer) checkDatasourceHealth(c *models.ReqContext, ds *datasource
 		}
 	}
 
-	proxyutil.ClearCookieHeader(c.Req, ds.AllowedCookies())
+	proxyutil.ClearCookieHeader(c.Req, ds.AllowedCookies(), []string{hs.Cfg.LoginCookieName})
 	if cookieStr := c.Req.Header.Get("Cookie"); cookieStr != "" {
 		req.Headers["Cookie"] = cookieStr
 	}