[MM-38216] Add API endpoint and adapt search to allow multi-team search (#18371)

* Add API endpoint and adapt search to allow multi-team search

* Refactor handler, refactor sql query to use squirrel, rename app and store functions and add tests

* Fix lint

* Fix search engines and remove unneeded comments

* Fix test

* Remove user from channel after test

api4/post_test.go

@@ -2201,6 +2201,11 @@ func TestSearchPosts(t *testing.T) {
 	_ = th.CreateMessagePostWithClient(th.Client, archivedChannel, "#hashtag for post3")
 	th.Client.DeleteChannel(archivedChannel.Id)
 
+	otherTeam := th.CreateTeam()
+	channelInOtherTeam := th.CreateChannelWithClientAndTeam(th.Client, model.ChannelTypeOpen, otherTeam.Id)
+	_ = th.AddUserToChannel(th.BasicUser, channelInOtherTeam)
+	_ = th.CreateMessagePostWithClient(th.Client, channelInOtherTeam, "search for post 5")
+
 	terms := "search"
 	isOrSearch := false
 	timezoneOffset := 5
@@ -2209,6 +2214,18 @@ func TestSearchPosts(t *testing.T) {
 		IsOrSearch:     &isOrSearch,
 		TimeZoneOffset: &timezoneOffset,
 	}
+	allTeamsPosts, _, err := client.SearchPostsWithParams("", &searchParams)
+	require.NoError(t, err)
+	require.Len(t, allTeamsPosts.Order, 4, "wrong search along multiple teams")
+
+	terms = "search"
+	isOrSearch = false
+	timezoneOffset = 5
+	searchParams = model.SearchParameter{
+		Terms:          &terms,
+		IsOrSearch:     &isOrSearch,
+		TimeZoneOffset: &timezoneOffset,
+	}
 	posts, _, err := client.SearchPostsWithParams(th.BasicTeam.Id, &searchParams)
 	require.NoError(t, err)
 	require.Len(t, posts.Order, 3, "wrong search")