PLT-3893: Structured Logging Continues (#7252)

* PLT-3893: Imported logger work from https://github.com/MusikPolice/platform

* PLT-3893: Integrated logger with system config

* PLT-3893: Integrated Mattermost config with logging solution, modified log message serialization so entire message is serialized as a JSON object

* PLT-3893: Added support for format strings in Debug methods. Added an overload that does not require a Context object for cases when one isn't available

* PLT-3893: Added context and format string support to debug and error methods

* PLT-3893: A few updates from pull request feedback

* PLT-3893: Changed tests to use testify

* Fixed TestAddRemoveConfigListener to no longer assume that there are zero config listeners when the test begins, since other tests could add config listeners

* Updated TestGetDeletedChannelsForTeam so that it doesn't assume state when it begins

* PLT-3893: Changed File property of log message so that it's relative to /mattermost directory, rather than to wherever the user is running the application from on their machine

* Flipped expected/actual assert arguments, added an explicit test for getCallerFilename(...), since it's failing on Jenkins

* Added printlns to debug failing tests on Jenkins

* Relaxed test cases to avoid failure on Jenkins caused by code coverage calculations. Removed printlns.

* Changed the way that caller filename is determined to make it more robust, updated tests to make them more lax, while not choking on the strange paths that Jenkins uses.

* Fixed gofmt issues

* Added debug output to tests to diagnose Jenkins build failures

* Still trying to get some useful debug logging on Jenkins

* Changed getCallerFilename to handle the strange paths that runtime.Caller(...) returns on Jenkins

* Fixing checkstyle issues

api4/channel_test.go

@@ -502,9 +502,7 @@ func TestGetDeletedChannelsForTeam(t *testing.T) {
 
 	channels, resp = Client.GetDeletedChannelsForTeam(team.Id, 0, 100, "")
 	CheckNoError(t, resp)
-	if len(channels) != 0 {
-		t.Fatal("should be no deleted channels")
-	}
+	numInitialChannelsForTeam := len(channels)
 
 	// create and delete public channel
 	publicChannel1 := th.CreatePublicChannel()
@@ -512,7 +510,7 @@ func TestGetDeletedChannelsForTeam(t *testing.T) {
 
 	channels, resp = Client.GetDeletedChannelsForTeam(team.Id, 0, 100, "")
 	CheckNoError(t, resp)
-	if len(channels) != 1 {
+	if len(channels) != numInitialChannelsForTeam+1 {
 		t.Fatal("should be 1 deleted channel")
 	}
 
@@ -521,7 +519,7 @@ func TestGetDeletedChannelsForTeam(t *testing.T) {
 
 	channels, resp = Client.GetDeletedChannelsForTeam(team.Id, 0, 100, "")
 	CheckNoError(t, resp)
-	if len(channels) != 2 {
+	if len(channels) != numInitialChannelsForTeam+2 {
 		t.Fatal("should be 2 deleted channels")
 	}