Backport: SPI for loading ABC templates (#14659)

[mgodwan]

• SPI for loading ABC templates
• Backport for SPI for loading ABC templates #14659

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

❌ Gradle check result for 77f7604: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for 577f181: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for c4f8717: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

✅ Gradle check result for 317e512: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 84.39716% with 22 lines in your changes missing coverage. Please review.

Project coverage is 71.68%. Comparing base (a6b8be1) to head (317e512).
Report is 2 commits behind head on 2.x.

Files	Patch %	Lines
...r/applicationtemplates/SystemTemplatesService.java	83.58%	8 Missing and 3 partials ⚠️
...r/applicationtemplates/SystemTemplateMetadata.java	62.50%	6 Missing ⚠️
...iontemplates/ClusterStateSystemTemplateLoader.java	89.18%	2 Missing and 2 partials ⚠️
server/src/main/java/org/opensearch/node/Node.java	83.33%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x   #14784      +/-   ##
============================================
+ Coverage     71.58%   71.68%   +0.09%     
- Complexity    62462    62604     +142     
============================================
  Files          5106     5111       +5     
  Lines        293563   293709     +146     
  Branches      42772    42783      +11     
============================================
+ Hits         210160   210541     +381     
+ Misses        65744    65478     -266     
- Partials      17659    17690      +31     

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