Clarify a few items in the docs

[discdiver]

• Adds note and links for other ways to limit concurrency.
• Adds a note on what the max_workers param does in task runner example.
• Minor formatting updates for style consistency.

Checklist

• This pull request references any related issue by including "closes <link to issue>"
  • If no issue exists and your change is not a small fix, please create an issue first.
• If this pull request adds new functionality, it includes unit tests that cover the changes
• If this pull request removes docs files, it includes redirect settings in mint.json.
• If this pull request adds functions or classes, it includes helpful docstrings.

cc: @kevingrismore - following up on your note from PACC re: max_workers

[discdiver]

Merging as the two test failures are unrelated to these pages changed.

FAILED docs/3.0/develop/artifacts.mdx::/home/runner/work/prefect/prefect/docs/3.0/develop/artifacts.mdx
FAILED docs/3.0/automate/events/automations-triggers.mdx::/home/runner/work/prefect/prefect/docs/3.0/automate/events/automations-triggers.mdx