Baseline MAINTAINERS and CODEOWNERS with active maintainers

[dbwiddis]

Description

Updates MAINTAINERS and CODEOWNERS with non-active maintainers moved to emeritus.

Issues Resolved

Fixes #448 (and its doppelgänger #449)

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[codecov-commenter]

Codecov Report

Merging #460 (6319400) into main (514f796) will decrease coverage by 0.17%.
The diff coverage is n/a.

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@@             Coverage Diff              @@
##               main     #460      +/-   ##
============================================
- Coverage     62.32%   62.16%   -0.17%     
+ Complexity      159      158       -1     
============================================
  Files            30       30              
  Lines           730      740      +10     
  Branches         20       21       +1     
============================================
+ Hits            455      460       +5     
- Misses          266      270       +4     
- Partials          9       10       +1     

Impacted Files	Coverage Δ
...ain/java/org/opensearch/sdk/ExtensionSettings.java	82.75% <0.00%> (-11.98%)	⬇️
...rc/main/java/org/opensearch/sdk/BaseExtension.java	84.61% <0.00%> (-7.70%)	⬇️
...main/java/org/opensearch/sdk/ExtensionsRunner.java	68.38% <0.00%> (ø)

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