build(client): Release notes and changelogs generation for minor release 2.81.0 (#26253)

build(client): Release notes and changelogs generation for minor release
2.81.0.
Ran command:
1.) pnpm flub generate releaseNotes -g client -t minor --outFile
RELEASE_NOTES/2.81.0.md
2.) pnpm flub generate changelog -g client

3.) Manually fixed the Release note file to move the Start Building
Today! in a separate section and move inside main contents. We can fix
the build tools in separate PR.

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Co-authored-by: Jatin Garg <jatingarg@Jatins-MacBook-Pro-2.local>

Author: jatgarg