[Backport 2.x] Fix missing order field in TemplatesMetadata deserialization

[opensearch-trigger-bot]

Backport bcd09ab from #15509.

[github-actions]

❕ Gradle check result for 0b0460c: UNSTABLE

• TEST FAILURES:

      1 org.opensearch.cluster.MinimumClusterManagerNodesIT.testThreeNodesNoClusterManagerBlock

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 71.54%. Comparing base (202eddf) to head (0b0460c).
Report is 6 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...opensearch/cluster/metadata/TemplatesMetadata.java	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##                2.x   #15591   +/-   ##
=========================================
  Coverage     71.54%   71.54%           
- Complexity    63849    63887   +38     
=========================================
  Files          5239     5239           
  Lines        299071   299070    -1     
  Branches      43539    43539           
=========================================
+ Hits         213970   213972    +2     
- Misses        67154    67187   +33     
+ Partials      17947    17911   -36     

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