MM-8796: Full implementation of "Schemes" in Store/Model/App layers. (#8357)

* Add Scheme model and stub store.

* Port ChannelStore to be Scheme aware.

* Make almost all the API/APP layer work with ChannelSchemes.

Only thing still hacky is UpdateChannelMemberRoles().

* Add basic SchemeStore implementation.

* Migrate UpdateChannelMemberRoles properly and fix tests.

* Update store tests and mocks so they work.

* Include creating default roles in Scheme create store function.

* Implement role deletion and start scheme deletion.

* Only use non-deleted roles for authorization.

* Add GetByScheme method to Team store.

* Add GetChannelsByScheme.

* Update store mocks.

* Implement scheme deletion in the store.

* Rename is valid function.

* Add offset and limit to queries to fetch teams and channels by scheme.

* Fix queries.

* Implement scheme awareness in Team store and add a migration.

* Tidy up ChannelStore mapping functions and add exhaustive unit tests.

* Add all missing i18n.

* Proper tests for TeamStore internal functions and fix them.

* Make additional TeamMember fields nullable.

* Make new ChannelMember fields nullable.

* Create new nullable columns without defaults.

* Make new fields in large tables nullalble.

* Fix empty list of TeamMembers.

* Deduplicate SQL queries.

* Fix spelling.

* Fix review comment.

* More review fixes.

* More review fixes.

model/scheme.go

@@ -0,0 +1,95 @@
+// Copyright (c) 2018-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package model
+
+import (
+	"encoding/json"
+	"io"
+)
+
+const (
+	SCHEME_NAME_MAX_LENGTH        = 64
+	SCHEME_DESCRIPTION_MAX_LENGTH = 1024
+	SCHEME_SCOPE_TEAM             = "team"
+	SCHEME_SCOPE_CHANNEL          = "channel"
+)
+
+type Scheme struct {
+	Id                      string `json:"id"`
+	Name                    string `json:"name"`
+	Description             string `json:"description"`
+	CreateAt                int64  `json:"create_at"`
+	UpdateAt                int64  `json:"update_at"`
+	DeleteAt                int64  `json:"delete_at"`
+	Scope                   string `json:"scope"`
+	DefaultTeamAdminRole    string `json:"default_team_admin_role"`
+	DefaultTeamUserRole     string `json:"default_team_user_role"`
+	DefaultChannelAdminRole string `json:"default_channel_admin_role"`
+	DefaultChannelUserRole  string `json:"default_channel_user_role"`
+}
+
+func (scheme *Scheme) ToJson() string {
+	b, _ := json.Marshal(scheme)
+	return string(b)
+}
+
+func SchemeFromJson(data io.Reader) *Scheme {
+	var scheme *Scheme
+	json.NewDecoder(data).Decode(&scheme)
+	return scheme
+}
+
+func (scheme *Scheme) IsValid() bool {
+	if len(scheme.Id) != 26 {
+		return false
+	}
+
+	return scheme.IsValidForCreate()
+}
+
+func (scheme *Scheme) IsValidForCreate() bool {
+	if len(scheme.Name) == 0 || len(scheme.Name) > SCHEME_NAME_MAX_LENGTH {
+		return false
+	}
+
+	if len(scheme.Description) > SCHEME_DESCRIPTION_MAX_LENGTH {
+		return false
+	}
+
+	switch scheme.Scope {
+	case SCHEME_SCOPE_TEAM, SCHEME_SCOPE_CHANNEL:
+	default:
+		return false
+	}
+
+	if !IsValidRoleName(scheme.DefaultChannelAdminRole) {
+		return false
+	}
+
+	if !IsValidRoleName(scheme.DefaultChannelUserRole) {
+		return false
+	}
+
+	if scheme.Scope == SCHEME_SCOPE_TEAM {
+		if !IsValidRoleName(scheme.DefaultTeamAdminRole) {
+			return false
+		}
+
+		if !IsValidRoleName(scheme.DefaultTeamUserRole) {
+			return false
+		}
+	}
+
+	if scheme.Scope == SCHEME_SCOPE_CHANNEL {
+		if len(scheme.DefaultTeamAdminRole) != 0 {
+			return false
+		}
+
+		if len(scheme.DefaultTeamUserRole) != 0 {
+			return false
+		}
+	}
+
+	return true
+}