Update performance-focused Swift server guides

[heckj]

Update performance focused Swift server guides

The existing Swift Server guides are a bit outdated and need to be updated or deprecated as appropriate.
If the Docs repository proposal (& #1189 ) is accepted, then we the content may need migrating to another repository as well.

While doing that proposal planning and analysis, I started a review to coordinate with the @swiftlang/server-workgroup, captured in https://hackmd.io/FFykBZmhS2-t8HBJVg9Lrg

Details

This issue is to track review/analysis and migration and/or updating progress for the existing content as it relates to performance analysis and optimization for servers:

• performance (current)
• linux-perf (current)
• memory leaks and usage (current)
• allocations (current)