Add skip on no changes option

[imbyungjun]

Hi,
I'm using jacoco-report action well, but I need a simple option, so I made a PR.

I wish I could skip adding a comment if the file coverage is not changed.
So, I added a simple option skip-on-no-changes.

In my case, use jacoco-report action multiple times to get coverage for each modules like..

- name: A Coverage
  uses: madrapps/[email protected]
  with:
    title: "A Coverage"
    paths: ${{ github.workspace }}/module-A/build/reports/jacoco/testCoverage/testCoverage.xml
    ...

- name: B Coverage
  uses: madrapps/[email protected]
  with:
    title: "B Coverage"
    paths: ${{ github.workspace }}/module-B/build/reports/jacoco/testCoverage/testCoverage.xml
    ...

It makes to add all the comments for each modules even if there's no file coverage changed on a module.
If the skip-on-no-changes option is available, a module that file coverage is not changed can be out of PR context by skipping to add a comment.

[thsaravana]

@imbyungjun Thank you for PR. I am working on adding native multi-module support. So probably I might tweak the behavior of this flag a bit.