Expand environment variables for sparse checkout path

[raghavgarg098]

JENKINS-23477

Expand environment variables in sparse checkout path using pattern matching to look for environment variables name.

Checklist

• [x] I have read the CONTRIBUTING doc
• [x] I have referenced the Jira issue related to my changes in one or more commit messages
• [x] I have added tests that verify my changes
• [x] Unit tests pass locally with my changes
• [ ] I have added documentation as necessary
• [x] No Javadoc warnings were introduced with my changes
• [x] No spotbugs warnings were introduced with my changes
• [x] Documentation in README has been updated as necessary
• [ ] Online help has been added and reviewed for any new or modified fields
• [ ] I have interactively tested my changes
• [ ] Any dependent changes have been merged and published in upstream modules (like git-client-plugin)

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)