[FORWARDPORT 2.x] Add 2.19 release notes

[jainankitk]

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[jainankitk]

@reta - I am confused while forward porting to main. For example:

Why the CHANGELOG.md entry - Latency and Memory allocation improvements to Multi Term Aggregation queries (#14993) is not there in 2.x branch. As per my understanding, if it is not relevant for 2.x, should have been part of CHANGELOG-3.0.md?

[reta]

@reta - I am confused while forward porting to main. For example:

@jainankitk seems like backport has failed [1] and no one took any actions :(

[1] #14993 (comment)

[jainankitk]

@reta - I am confused while forward porting to main. For example:

@jainankitk seems like backport has failed [1] and no one took any actions :(

[1] #14993 (comment)

There is possibility of unliked PR, but given changelog is missing in 2.x, chances are low. So, from the release notes perspective, main CHANGELOG.md should be exactly same as 2.x, except if there are commits in the meantime. Anything meant for 3.x only, should just be part of CHANGELOG-3.0.md

[reta]

So, from the release notes perspective, main CHANGELOG.md should be exactly same as 2.x, except if there are commits in the meantime.

Correct, if backport was done (manually or automatically)

Anything meant for 3.x only, should just be part of CHANGELOG-3.0.md

Correct

[jainankitk]

main: #17317