Check broken links automatically

[saratvemulapalli]

As we are dynamic and things are fluid, links to other repositories might become broken.
Here is an example PR: #26

Developers find these problems when they use to documentation, but we should have an automated way to check and notify broken links.
This is probably needed for all the project i.e OpenSearch/Dashboards, plugins repo and all the plugins too.

One quick solution I could find was using github actions: https://github.com/marketplace/actions/broken-link-check.

[saratvemulapalli]

Thanks @VachaShah for taking care of this.
Closing this issue.