bump version for first beta of 1.5.2

Merge pull request desktop#6455 from desktop/i-told-you-i-didnt-have-…

…conflicts

Backport work from PR desktop#6452

Update changelog.json

1.5.1-beta5

Update changelog.json

Add release notes

that attribution tho

Co-Authored-By: Neha Batra <[email protected]>

1.5.1-beta1 release notes

beta bump

Apply suggestions from code review

Co-Authored-By: outofambit <[email protected]>