[Feature] Support .issuetracker file

It would be great if SourceGit would support automatic issue tracker setup by checking for a `.issuetracker` file in the repo root dir.

Example of a `.issuetracker` file:
```ini
# Integration with Issue Tracker
#
# (note that '\' need to be escaped).

[issuetracker "Azure DevOps"]
  regex = "#(\\d+)"
  url = "https://dev.azure.com/<yourname>/_workitems/edit/$1"
```
