Updated principal-key/features/functions.md based on AA feedback

[Andriciuc]

In set-principal-key.md:

• updated with correct code example using set_server_key_using_global parameter
• updated note to reflect correct config

In features.md:

• Removed temporary tables feature to clear confusion, removed logical replication mention, removed WAL encryption as a feature.

In functions.md:

• Added ON FUNCTION for grant/revoke execution
• Modified sensitive info bolded paragraph to important note
• Small modifications to notes display, title cases and text fixes
• added note to Add or modify Vault providers for keeping the same principal key.
• Added warning for WAL in pg_tde_create_key_using_global_key_provider

In general:

• Removed all logical replication mentions except the FAQ and in RC2 release note.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (release-17.5.2@8b1f1cf). Learn more about missing BASE report.

Additional details and impacted files

@@                Coverage Diff                @@
##             release-17.5.2     #441   +/-   ##
=================================================
  Coverage                  ?   84.68%           
=================================================
  Files                     ?       21           
  Lines                     ?     2593           
  Branches                  ?      401           
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  Hits                      ?     2196           
  Misses                    ?      316           
  Partials                  ?       81           

Components	Coverage Δ
access	81.11% <0.00%> (?)
catalog	88.22% <0.00%> (?)
common	77.77% <0.00%> (?)
encryption	73.45% <0.00%> (?)
keyring	72.88% <0.00%> (?)
src	91.54% <0.00%> (?)
smgr	94.85% <0.00%> (?)
transam	∅ <0.00%> (?)

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