jgit timestamp provider should support fetching the history from the remote

[laeubi]

This is a followup on

• https://github.com/eclipse-tycho/tycho/issues/947

Problem:

Currently when using a shallow copy (often used for CI builds) the timestamps do not work reliable leading to strange effects, we improved it already here to give an error/warning so users are not confused:

• https://github.com/eclipse-tycho/tycho/pull/5507

But as shallow copies are still useful (e.g. let storage, less to checkout), we want another option now:

• add a new option beside ERROR, WARNING, IGNORE that is REMOTE
• if REMOTE is enabled we should fetch the history from the remote origin instead of using the local history for the project folder
• REMOTE should become the new default and we should print a message to the log when this is used.