Validate provider IDs

[felixarntz]

Only allow lower-case alphanumeric characters, hyphens, and underscores.

[gziolo]

Thank you for a quick follow up 👍🏻

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: felixarntz <flixos90@git.wordpress.org>
Co-authored-by: gziolo <gziolo@git.wordpress.org>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.12%. Comparing base (2d6efec) to head (77578a8).
⚠️ Report is 3 commits behind head on trunk.

Additional details and impacted files

@@             Coverage Diff              @@
##              trunk     #221      +/-   ##
============================================
+ Coverage     88.11%   88.12%   +0.01%     
- Complexity     1212     1213       +1     
============================================
  Files            60       60              
  Lines          3928     3934       +6     
============================================
+ Hits           3461     3467       +6     
  Misses          467      467              

Flag	Coverage Δ
unit	88.12% <100.00%> (+0.01%)	⬆️

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