docs: reorganize docs to highlight tools and drivers

[amoeba]

This is a major reorganization and rethinking of the ADBC docs to catch them up with what's happening across the ADBC ecosystem.

The key changes are:

• New, simpler landing page focusing on the core questions users will have (what drivers are available, how do I connect with one, how do I write a new driver)
• New sidebar structure that starts by grouping pages into one of two major categories: Connecting or Writing Drivers
• New Drivers page that covers the third-party driver ecosystem which has grown quite a lot. Includes talking about dbc, the ADBC Driver Foundry, third-party drivers offered by Columnar
• New Tools & Integrations page covering the cool ecosystem stuff like pandas/polars/R/etc
• Now uses the term "Client Library" over Driver Manager in many places as this is conceptually more simple. No packages were renamed so the term Driver Manager is still valid and used in the docs.
• Language-specific docs now more consistently load drivers by manifest rather than driver-specific packages.
• New page on Writing Drivers
• New page on Connection Profiles
• A small but updated C# page
• Updated Glossary

TODOs before merge (if possible):

• [Ian] Fix R index and quickstart
• [Ian] Fix Ruby index and quickstart
• Confirm with MS team about docs: reorganize docs to highlight tools and drivers #4525 (comment)

Closes #4233
Closes #4454

[ianmcook]

Should we update the driver installation instructions the Go README to be more consistent with the other language quickstarts updated here?
https://pkg.go.dev/github.com/apache/arrow-adbc/go/adbc#section-readme

EDIT: Done in 1badce5

[ianmcook]

Should we update the driver installation instructions the Go README to be more consistent with the other language quickstarts updated here? https://pkg.go.dev/github.com/apache/arrow-adbc/go/adbc#section-readme

Done in 1badce5