Remove submodules dependency from data extension editor

[norascheuch]

Instead of creating a new temporary folder with dependency files every time we fetch the external api usage, we do this only once now during startup of the editor. This is also the time when we now install pack dependencies and thus remove dependency on submodules.

Checklist

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.

[robertbrignull]

I've looked through the code but haven't tested it yet. I'll give it a go a bit later on. I have a couple of small suggestions to make the code easier to read, but overall the change looks good to me.

[robertbrignull]

I've tested it out, both in a codespace and locally in a repo without the QL submodule. It worked in both cases! 🎉 🌮

[robertbrignull]

A couple of comments which you could address or leave, but generally I think this PR is ok and it works well for me when testing it.