Use merge target when creating pull requests

[eamodio]

Description

We should be leveraging the merge target when creating pull requests

[sergeibbb]

@eamodio

If gk-merge-base is defined in .git/config then it works well. ✅

⚠️ One thing looks like a problem. For branches that do not have merge branch in .git/config it opens PRs creation agains themselves.

Steps to reproduce:

1. Have a branch test that has remote and merge fields only in .git/config
2. Open in VSCode -> VSCode creates vscode-merge-base = origin/test
3. Click to "Create Pull Request"

Actual reasult:

GitLens creates gk-merge-base = origin/test and opens a PR creation page with the same branch on both sides:

[sergeibbb]

@eamodio @d13 Should I reopen this issue or will it go to a follow-up?

[eamodio]

Please reopen and could you look into the root cause?

[sergeibbb]

@eamodio

could you look into the root cause?

Sure.