Expose public/ API as submodule (#23345)

* model -> public/model

* plugin -> public/plugin

* public/model/utils -> public/utils

* platform/shared/mlog -> public/shared/mlog

* platform/shared/i18n -> public/shared/i18n

* platform/shared/markdown -> public/shared/markdown

* platform/services/timezones -> public/shared/timezones

* channels/einterfaces -> einterfaces

* expose public/ submodule

* go mod tidy

* .github: cache-dependency-path, setup-go-work

* modules-tidy for public/ too

* remove old gomodtidy

server/public/shared/timezones/timezones_test.go

@@ -0,0 +1,33 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package timezones
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestTimezoneConfig(t *testing.T) {
+	tz1 := New()
+	assert.NotEmpty(t, tz1.GetSupported())
+}
+
+func TestDefaultUserTimezone(t *testing.T) {
+	defaultTimezone := DefaultUserTimezone()
+	require.Equal(t, "true", defaultTimezone["useAutomaticTimezone"])
+	require.Empty(t, defaultTimezone["automaticTimezone"])
+	require.Empty(t, defaultTimezone["manualTimezone"])
+
+	defaultTimezone["useAutomaticTimezone"] = "false"
+	defaultTimezone["automaticTimezone"] = "EST"
+	defaultTimezone["manualTimezone"] = "AST"
+
+	defaultTimezone2 := DefaultUserTimezone()
+	require.Equal(t, "true", defaultTimezone2["useAutomaticTimezone"])
+	require.Empty(t, defaultTimezone2["automaticTimezone"])
+	require.Empty(t, defaultTimezone2["manualTimezone"])
+
+}