MM-24133: Migrate AppError from bot_store.go (#14339)

* MM-24135: Migrate AppError from SaveChannel/channel_store.go

This is the first POC of migration of store app errors to plain error.

We create a few basic error types in the store package and use
them to return the errors from store methods. In the app layer,
we inspect the error and re-create the exact app errors. This lets
us preserve the same error content, but yet move to plain errors.

Since this is a gradual migration, this means that the error inspection
code will be duplicated across the app layer whenever a store method
is invoked. But all of that should go away once we start propagating
the errors higher up the hierarchy.

There have been a significant amount of changes in the storetest and searchtest
layer, primarily because we have to rename the err variable now that it is of
a different type.

* Addressed review comments

* MM-24132: Migrate AppError from SaveDirectChannel/channel_store.go

This PR migrates 2 new methods SaveDirectChannel and CreateDirectChannel
to return error instead of AppError.

We also need to handle the error internally in SaveMultipleMember for now
until that is migrated too.

* MM-24133: Migrate AppError from bot_store.go

* Fix errors

* Fix err

* Fix bad return

* Fix vet errors

* Fix incorrect error check

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

store/searchtest/helper.go

@@ -218,10 +218,10 @@ func (th *SearchTestHelper) createBot(username, displayName, ownerID string) (*m
 	}
 
 	botModel.UserId = user.Id
-	bot, apperr := th.Store.Bot().Save(botModel)
-	if apperr != nil {
+	bot, err := th.Store.Bot().Save(botModel)
+	if err != nil {
 		th.Store.User().PermanentDelete(bot.UserId)
-		return nil, errors.New(apperr.Error())
+		return nil, errors.New(err.Error())
 	}
 
 	return bot, nil

store/searchtest/user_layer.go

@@ -497,6 +497,7 @@ func testAutocompleteUserByUsernameWithHyphen(t *testing.T, th *SearchTestHelper
 func testShouldEscapePercentageCharacter(t *testing.T, th *SearchTestHelper) {
 	userAlternate, err := th.createUser("alternateusername", "alternate%nickname", "firstname", "altlastname")
 	require.Nil(t, err)
+
 	defer th.deleteUser(userAlternate)
 	err = th.addUserToTeams(userAlternate, []string{th.Team.Id})
 	require.Nil(t, err)
@@ -641,6 +642,7 @@ func testSearchUsersShouldBeCaseInsensitive(t *testing.T, th *SearchTestHelper)
 func testSearchOneTwoCharUsersnameAndFirstLastNames(t *testing.T, th *SearchTestHelper) {
 	userAlternate, err := th.createUser("ho", "alternatenickname", "zi", "k")
 	require.Nil(t, err)
+
 	defer th.deleteUser(userAlternate)
 	err = th.addUserToTeams(userAlternate, []string{th.Team.Id})
 	require.Nil(t, err)
@@ -668,6 +670,7 @@ func testShouldSupportKoreanCharacters(t *testing.T, th *SearchTestHelper) {
 	userAlternate, err := th.createUser("alternate-username", "alternate-nickname", "서강준", "안신원")
 	require.Nil(t, err)
 	defer th.deleteUser(userAlternate)
+
 	err = th.addUserToTeams(userAlternate, []string{th.Team.Id})
 	require.Nil(t, err)
 	_, err = th.addUserToChannels(userAlternate, []string{th.ChannelBasic.Id})