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/model/usage.go

@@ -0,0 +1,34 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+type PostsUsage struct {
+	Count int64 `json:"count"`
+}
+
+type StorageUsage struct {
+	Bytes int64 `json:"bytes"`
+}
+
+type TeamsUsage struct {
+	Active        int64 `json:"active"`
+	CloudArchived int64 `json:"cloud_archived"`
+}
+
+var InstalledIntegrationsIgnoredPlugins = map[string]struct{}{
+	PluginIdPlaybooks:     {},
+	PluginIdFocalboard:    {},
+	PluginIdApps:          {},
+	PluginIdCalls:         {},
+	PluginIdNPS:           {},
+	PluginIdChannelExport: {},
+}
+
+type InstalledIntegration struct {
+	Type    string `json:"type"` // "plugin" or "app"
+	ID      string `json:"id"`
+	Name    string `json:"name"`
+	Version string `json:"version"`
+	Enabled bool   `json:"enabled"`
+}