MM-43753: Module workspaces (#20113)

* MM-43753: Module workspaces

Move to module workspaces

We make the following changes:
- Remove the vendor directory.
- Dynamically create the go.work file if it doesn't exist.
- Set the MM_SERVER_PATH for enterprise tests.

https://mattermost.atlassian.net/browse/MM-43753

```release-note
NONE
```

* Fix missing reference to MM_SERVER_PATH

```release-note
NONE
```

* Update test to add another nested dir

```release-note
NONE
```

* Have separate script to create go.work file

```release-note
NONE
```

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

scripts/setup_go_work.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+
+if [[ ! -f "go.work" ]] ;
+then
+    echo "Creating a go.work file"
+    cat >go.work <<EOL
+go 1.18
+
+use ./
+
+use ../enterprise
+EOL
+fi