Chore: remove session storage references (#16445)

* Chore: remove session storage references

* Small refactoring of the settings module

* Update docs - remove references for the session storage

* Update config files (sample and default configs)

* Add tests for warning during the config load on defined storage cache

* Remove all references to session storage

* Remove macaron session dependency

* Remove leftovers

* Fix: address review comments

* Fix: remove old deps

* Fix: add skipStaticRootValidation = true to tests

* Fix: improve the docs and warning message

As per discussion in here - https://github.com/grafana/grafana/pull/16445/files#r273026255

* Chore: make linter happy

Fixes #16148
Ref #16114

pkg/setting/setting_session_test.go

@@ -0,0 +1,43 @@
+package setting
+
+import (
+	"path/filepath"
+	"testing"
+
+	"github.com/grafana/grafana/pkg/log"
+	. "github.com/smartystreets/goconvey/convey"
+)
+
+type testLogger struct {
+	log.Logger
+	warnCalled  bool
+	warnMessage string
+}
+
+func (stub *testLogger) Warn(testMessage string, ctx ...interface{}) {
+	stub.warnCalled = true
+	stub.warnMessage = testMessage
+}
+func TestSessionSettings(t *testing.T) {
+	Convey("session config", t, func() {
+		skipStaticRootValidation = true
+
+		Convey("Reading session should log error ", func() {
+			var (
+				cfg      = NewCfg()
+				homePath = "../../"
+			)
+
+			stub := &testLogger{}
+			cfg.Logger = stub
+
+			cfg.Load(&CommandLineArgs{
+				HomePath: homePath,
+				Config:   filepath.Join(homePath, "pkg/setting/testdata/session.ini"),
+			})
+
+			So(stub.warnCalled, ShouldEqual, true)
+			So(len(stub.warnMessage), ShouldBeGreaterThan, 0)
+		})
+	})
+}