feat: added no-merge flag to sync, diff, apply command

[Prashansa-K]

--no-merge flag enables deck to process the
files passed one by one, rather than merging
them all together and send as a whole.
This is useful in case entities are split
across multiple files with different
select-tags. Merging would tag all entities
with the mentioned select-tags. A no-merge
option bypasses this issue. It also keeps our
request urls sent to admin-api under maxLength

Basing this over 3.13 and 3.14 branch tests branch and tests/konnect to avoid conflicts later.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 166 lines in your changes missing coverage. Please review.
✅ Project coverage is 32.14%. Comparing base (c07059f) to head (2767d6d).
⚠️ Report is 18 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/common.go	0.00%	68 Missing ⚠️
cmd/gateway_diff.go	0.00%	23 Missing ⚠️
cmd/utils.go	0.00%	22 Missing ⚠️
cmd/gateway_sync.go	0.00%	21 Missing ⚠️
cmd/gateway_validate.go	0.00%	19 Missing ⚠️
cmd/gateway_apply.go	0.00%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1994      +/-   ##
==========================================
- Coverage   32.92%   32.14%   -0.79%     
==========================================
  Files          77       77              
  Lines        6988     7149     +161     
==========================================
- Hits         2301     2298       -3     
- Misses       4504     4667     +163     
- Partials      183      184       +1     

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[Prashansa-K]

Holding off on merge:
This is a basic usecase here.
The following issues still exist:

• If a directory is passed deck gateway sync dirname --no-merge, files aren't executed without merge.
• diff and validate don't check for "duplicates" yet.

[gitguardian]

️✅ There are no secrets present in this pull request anymore.

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[Prashansa-K]

Will add more tests to this to cover directory traversal and duplicates checking.
Need to update validate and apply workflows to account for batching as well.