Make matrix-project optional dependency

[jonesbusy]

What feature do you want to see added?

In a 100% pipeline Jenkins this plugin should not force installing the matrix-project.

Please consider making it optional

Similar to jenkinsci/htmlpublisher-plugin#287

Upstream changes

No response

Are you interested in contributing this feature?

No response

[jglick]

This plugin is not useful with Pipeline to begin with, but still it is preferable to avoid hard deps.

[damianszczepanik]

I'm happy to merge PR for this if only you can test it well with the matrix project