Add 2.0.0 release notes

[lezzago]

Signed-off-by: Ashish Agrawal [email protected]

Issue #, if available:
#439
Description of changes:
Add 2.0.0 release notes
CheckList:

• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
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[codecov-commenter]

Codecov Report

Merging #456 (70dfc2f) into main (32b336d) will decrease coverage by 0.10%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##               main     #456      +/-   ##
============================================
- Coverage     76.86%   76.75%   -0.11%     
  Complexity      176      176              
============================================
  Files           166      166              
  Lines          8369     8369              
  Branches       1231     1231              
============================================
- Hits           6433     6424       -9     
- Misses         1330     1340      +10     
+ Partials        606      605       -1     

Impacted Files	Coverage Δ
.../alerting/transport/TransportIndexMonitorAction.kt	68.18% <0.00%> (-3.15%)	⬇️
.../kotlin/org/opensearch/alerting/util/IndexUtils.kt	70.83% <0.00%> (-2.09%)	⬇️
...destinationmigration/DestinationConversionUtils.kt	70.00% <0.00%> (-1.12%)	⬇️
...ain/kotlin/org/opensearch/alerting/AlertService.kt	77.99% <0.00%> (-0.48%)	⬇️
...ing/model/destination/DestinationContextFactory.kt	78.57% <0.00%> (+3.57%)	⬆️
...nationmigration/DestinationMigrationCoordinator.kt	68.08% <0.00%> (+4.25%)	⬆️

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