Add an option to create a shallow clone in gitPublishReset

[marcphilipp]

We use your excellent plugins to publish documentation and Javadoc to GH Pages in the junit5 repo. As you can see in this build scan, gitPublishReset takes most of the time of this build that was executed by a Travis job.

For our purposes a shallow clone of the single gh-pages branch would be sufficent to publish to our branch. This is probably not true for every project, but a configuration option that triggers the use of the grgit/JGit equivalent of --single-branch --depth=1 would really speed up our build.

[marcphilipp]

Looks like it isn't possible with JGit at the moment... ajoberstar/grgit#155

[shevek]

Similarly an option to clone using a local reference repository for the bulk of the data transfer might help?

[ajoberstar]

@shevek See #1 for the local repo idea. Seems like it could help a lot for bigger projects that already have that data cloned.

[liza-mae]

Any update on whether this will be supported?

[marcphilipp]

@ajoberstar Thanks for this! In JUnit's build, gitPublishReset went down from 3m 38s to 1m 13s. 🎉

[ajoberstar]

Thanks to @AfzalivE for sending the original PR adding support to grgit!