Change the plugin name and the yaml file name for future compatibility

[gautamabhishek46]

See JENKINS-52663

[grandvizier]

Well, I don't think this comes close to meeting the acceptance criteria for JENKINS-52663

But with regards to being a small change that improves things, I think this PR is good. I'd just suggest changing the title Change the plugin name and the yaml file name for future compatibility to be more clear that you're just changing the default script name.

[kwhetstone]

I'm not seeing the plugin name change here. Also, I'd suggest flowing the name out on the list first before making the PR so you're not having to make this change again.

[gautamabhishek46]

Plugin name can be "YAML Pipeline Builder".
We can have the same repo and Gitter room, for now, I guess.
Alpha versions are independent of the actual release, hence they can exist as it is.