fix: Fix connection update bug on project_id

[thogarty]

• Update Connection's project attribute to be optional/computed
  • It being set from the API response, but not being computed would cause it to be reverted to null during subsequent terraform plans/applies when there was never an explicit project set in the config.
• Updated Connection SetMap entry to not set nil values from API response
• Updated projectToFabric and projectToTerra methods to remove code bloat
• Updating handling of project config in connection and network resources

[codecov-commenter]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (a2797d8) 63.11% compared to head (8260941) 45.73%.
Report is 59 commits behind head on main.

Files	Patch %	Lines
equinix/resource_fabric_connection.go	93.18%	2 Missing and 1 partial ⚠️

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Additional details and impacted files

@@             Coverage Diff             @@
##             main     #583       +/-   ##
===========================================
- Coverage   63.11%   45.73%   -17.38%     
===========================================
  Files          94       93        -1     
  Lines       18250    18164       -86     
===========================================
- Hits        11519     8308     -3211     
- Misses       6299     9724     +3425     
+ Partials      432      132      -300     

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[srushti-patl]

LGTM