Fix: Names the Experimental ESM support warning

[NormalGaussian]

Names the ESM experimental loading warning

What's the problem this PR addresses?

Simple justification: unnamed logs should be avoided

More complex justifiation:
Lots of workspaces now are esm by default. This warning will appear on all of them. While it is "true", there is a strong desire to filter it out so that it does not:

• cause others to ignore genuine warnings
• make identifying warnings in CI overly complex, (partially address [Bug?]: Cannot easily test for yarn install warnings in CI when using esm modules with pnp #7066)

Unnamed logs cannot be filtered.

How did you fix it?

I've added a new name for the warning, and made the warning use that name

Checklist

• I have read the Contributing Guide.
• I have set the packages that need to be released for my changes to be effective.
• I will check that all automated PR checks pass before the PR gets reviewed.

[NormalGaussian]

It may be desirable to use an EXPERIMENTAL name rather than one so specific?

[clemyan]

Yeah, probably EXPERIMENTAL to cover all experimental features.

[NormalGaussian]

I've updated it to be EXPERIMENTAL

[clemyan]

Please also add a simple description to packages/docusaurus/docs/advanced/01-general-reference/error-codes.mdx