Add merged argument to all_user_clusters

[andy31415]

When generating matter code, in some cases we do not care about cluster side - specifically clusters in matter have a single definition without client/server side.

Provide the ability to select all clusters and ignore the "side" part and not have client/server duplicates.

This is to enhance project-chip/connectedhomeip#30605 to not have duplicated cluster entries.

Changes

• support and document a "merged" side
• updated grouping to not consider side if side is merged
• made order by hard-coded because the doOrder was already hardcoded.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (5c472c0) 64.95% compared to head (2a73c9c) 64.95%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1216   +/-   ##
=======================================
  Coverage   64.95%   64.95%           
=======================================
  Files         187      187           
  Lines       19329    19327    -2     
  Branches     4127     4126    -1     
=======================================
- Hits        12555    12554    -1     
+ Misses       6774     6773    -1     

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