[3007.x][66799] Update master-cluster.rst Example Config

[kevin-andrew-wipro]

The Master Config example's file_roots and pillar_roots properties need the base property followed by a list of the directory. Otherwise, the Salt master shows an error in the logs.

What does this PR do?

Updates the documentation of the Master Cluster config.

I had to close #66822 in order to rebase my branch against 3007.x.

What issues does this PR fix or reference?

Incorrect example of the Master Cluster config.
Fixes 66799 [DOCS] Documentation Inconsistency

Previous Behavior

New Behavior

Based on the example of file_roots here:
https://docs.saltproject.io/en/latest/ref/configuration/master.html#file-roots

we add base: to the config.

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• [x ] Docs
• Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• Tests written/updated

Commits signed with GPG?

No

Please review Salt's Contributing Guide for best practices, including the
PR Guidelines.

See GitHub's page on GPG signing for more information about signing commits with GPG.

[kevin-andrew-wipro]

Hello, @twangboy , I have rebased against the 3007.x branch and tried to set the original PR to submit against the 3007.x branch. But in trying all of that, the PR got closed (#66822). So I had to open this new one.

[twangboy]

No worries I'll try to get this one in.

[welcome]

Congratulations on your first PR being merged! 🎉