fix(cmd): negative or zero parallelism

[manishsvk]

Summary

This change adds a checkParallelism helper so an invalid value is rejected up front with a usage error, before any state file is read or any request is sent to Kong. Valid values (>= 1) are unaffected.

Full changelog

• [Added checkParallelism helper in cmd/common.go]
• [Fix for --parallelism < 1 (covers gateway sync, diff, apply and validate commands)]
• [Updated go-database-reconciler version]
• [Added unit tests for checkParallelism (zero, negative, positive)]

Issues resolved

Fix #375

Testing

• Unit tests
• Manual testing on local gateway instance

[CLAassistant]

All committers have signed the CLA.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 34.12%. Comparing base (701be42) to head (da3269c).

Files with missing lines	Patch %	Lines
cmd/gateway_validate.go	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2114      +/-   ##
==========================================
+ Coverage   33.17%   34.12%   +0.94%     
==========================================
  Files          78       78              
  Lines        7433     7443      +10     
==========================================
+ Hits         2466     2540      +74     
+ Misses       4763     4669      -94     
- Partials      204      234      +30     

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[harshadixit12]

LGTM - will approve once CI is fixed

[Prashansa-K]

This should have a go.mod update with a new GDR version that has the changes added here:
Kong/go-database-reconciler#483

[harshadixit12]

This should have a go.mod update with a new GDR version that has the changes added here: Kong/go-database-reconciler#483

We skipped it because it was not strictly required - it can go with next gdr release IMO

let's do the GDR version bump as well