docs(config): add clarification for gitAuthor format to avoid obscure errors during commits.

[slonim-greg]

Changes

Add documentation clarification for gitAuthor config option.
Closes #23538

Context

The context for this change is documented in Issue 23538.

Bottom line:

If one supplies gitAuthor or overrides RENOVATE_GIT_AUTHOR , it is often important to supply both NAME and EMAIL according to RFC-5322.

Documentation (please check one with an [x])

• I have updated the documentation

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[rarkins]

I'm not sure every platform requires both name and email

[slonim-greg]

It would not hurt to include, however, to avoid similar problems, even when a platform does not require it, right?

[rarkins]

I prefer not to tell something is required if it's only required for edge cases or a subset of platforms

[slonim-greg]

It was a problem for our repository; Moreover, the default setting in the "standard issue" Renovate Runner repo has the name there.
We can change the docs language to say that if one encounters the problem I saw, this is what they should do.
In reality though, this is a pretty low hanging fruit and seems pretty innocuous to include if one overrides this config value.
Thoughts?