feat: implement progress monitor for monitor jgit command execution.

[DarkWeird]

Contains

ProgressMonitor classes for further integration.

How to test

Single-thread:

1. Integrate monitor to one of jgit commands. (how noted at javadoc)
2. runs this command

Multi-thread:

1. make one of jgit command to run in parallel
2. Integrate monitor to one of jgit commands. (how noted at javadoc)
3. runs this command