Updated MAINTAINERS.md format.

[dblock]

Coming from opensearch-project/.github#121, updated MAINTAINERS.md to match opensearch-project recommended format.

[dblock]

Looks like some CI has failed. This change has no code changes, can someone please take a look at that?

[Xtansia]

@dblock If we can get #98 merged, that'll solve the changelog and unreleased opensearch (1.x) woes.

[codecov-commenter]

Codecov Report

Merging #99 (c43bea1) into main (8432c58) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #99   +/-   ##
=======================================
  Coverage   42.28%   42.28%           
=======================================
  Files          50       50           
  Lines       28085    28085           
=======================================
  Hits        11877    11877           
  Misses      16208    16208           

Flag	Coverage Δ
integration	42.28% <ø> (ø)

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