revamp integration contributor guide and clean up other sections

[zzstoatzz]

among other detail additions and stylistic improvements

starts explicitly recommending uv in a couple places where power users are more likely to be looking, since it is a genuine game changer in many cases and in my opinion we ought to be recommending it to users (except in the most introductory of cases where we need to maximize compatibility, though eventually we'll have uv as a virtue of having prefect and it is also generally platform independent, which helps us) - and fwiw

this PR also renames Manage run metadata to Using client methods and hoists it out of "Configure runtime behavior" since that page is fundamentally about using the client, which is not only configuring runtime behavior (imo that section was becoming a catch all)

see updated sections

• "commands for power users" accordion in install page
• improving readability of "Interact with API" examples with PrefectClient
• completely rewrite old and incorrect "Contributing to Integrations" guide