Reduce heap size usage during unit tests

[vrozov]

opensearch-security pull request intake form

Please provide as much details as possible to get feedback/acceptance on your PR quickly

1. Category: (Enhancement, New feature, Bug fix, Test fix, Refactoring, Maintenance, Documentation)
   Maintenance

2. Github Issue # or road-map entry, if available:

3. Description of changes:
   Change fork heap size and use unpooled netty byte buffer allocator

4. Why these changes are required?
   Lower heap usage during CI to free up more memory for direct buffers

5. What is the old behavior before changes and new behavior after changes? (Please add any example/logs/screen-shot if available)

6. Testing done: (Please provide details of testing done: Unit testing, integration testing and manual testing)

7. TO-DOs, if any: (Please describe pending items and provide Github issues# for each of them)

8. Is it backport from main branch? (If yes, please add backport PR # and commits #)

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[codecov-commenter]

Codecov Report

Merging #1368 (2b535f7) into main (960d420) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##               main    #1368      +/-   ##
============================================
- Coverage     64.78%   64.77%   -0.01%     
+ Complexity     3204     3203       -1     
============================================
  Files           247      247              
  Lines         17252    17252              
  Branches       3053     3053              
============================================
- Hits          11176    11175       -1     
  Misses         4526     4526              
- Partials       1550     1551       +1     

Impacted Files	Coverage Δ
...a/org/opensearch/security/tools/SecurityAdmin.java	47.26% <0.00%> (-0.27%)	⬇️
.../dlic/auth/ldap2/LDAPConnectionFactoryFactory.java	57.25% <0.00%> (+0.76%)	⬆️

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[davidlago]

Continuing in #1610