[Backport 2.x] Updated MAINTAINERS.md format.

[opensearch-trigger-bot]

Backport b49a36b from #771

[codecov-commenter]

Codecov Report

Merging #772 (b49a36b) into 2.x (8ce4493) will increase coverage by 0.01%.
The diff coverage is 78.93%.

❗ Current head b49a36b differs from pull request most recent head a6fa9f3. Consider uploading reports for the commit a6fa9f3 to get more accurate results

@@             Coverage Diff              @@
##                2.x     #772      +/-   ##
============================================
+ Coverage     79.43%   79.45%   +0.01%     
+ Complexity     4293     4273      -20     
============================================
  Files           302      301       -1     
  Lines         17956    17903      -53     
  Branches       1906     1886      -20     
============================================
- Hits          14263    14224      -39     
+ Misses         2790     2780      -10     
+ Partials        903      899       -4     

Flag	Coverage Δ
plugin	79.45% <78.93%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
.../main/java/org/opensearch/ad/NodeStateManager.java	74.50% <ø> (-0.66%)	⬇️
.../java/org/opensearch/ad/cluster/ADVersionUtil.java	93.33% <ø> (+5.83%)	⬆️
...in/java/org/opensearch/ad/model/ADTaskProfile.java	84.38% <0.00%> (ø)
.../java/org/opensearch/ad/model/AnomalyDetector.java	92.30% <ø> (ø)
...opensearch/ad/ratelimit/CheckpointWriteWorker.java	91.25% <0.00%> (ø)
...nsearch/ad/ratelimit/RateLimitedRequestWorker.java	71.22% <0.00%> (ø)
...a/org/opensearch/ad/rest/AbstractSearchAction.java	57.50% <0.00%> (ø)
...arch/ad/rest/RestExecuteAnomalyDetectorAction.java	26.82% <ø> (ø)
...nsearch/ad/rest/RestSearchAnomalyResultAction.java	23.80% <0.00%> (ø)
...ensearch/ad/transport/ADCancelTaskNodeRequest.java	100.00% <ø> (ø)
... and 93 more