Mark v1.17.0-rc2 in the changelog and release notes.

[SpicyLemon]

Description

Mark v1.17.0-rc2 in the changelog and release notes.

I accidentally made this change directly to release/v1.17.x and pushed it up. Since we can't push --force, I then reverted it and pushed that up to get the branch back to where it was before. Then I created this branch with the change so it could be PRd and merged like it should be.

---

Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer
• Review Codecov Report in the comment section below once CI passes