chore(CHANGELOG): add changelogs for v2.7.0

What this PR does?: This PR adds changelog for v2.7.0 release.

Does this PR require any upgrade changes?:

If the changes in this PR are manually verified, list down the scenarios covered and commands you used for testing with logs:

Any additional information for your reviewer?: Mention if this PR is part of any design or a continuation of previous PRs

Checklist:

[ ] Fixes #
[ ] PR Title follows the convention of <type>(<scope>): <subject>
[ ] Has the change log section been updated?
[ ] Commit has unit tests
[ ] Commit has integration tests
[ ] (Optional) Are upgrade changes included in this PR? If not, mention the issue/PR to track:
[ ] (Optional) If documentation changes are required, which issue on https://github.com/openebs/openebs-docs is used to track them:

openebs / velero-plugin