Add Rekor 1.0 CHANGELOG (sigstore#1122)

* Add Rekor 1.0 CHANGELOG

Signed-off-by: Priya Wadhwa <priya@chainguard.dev>

* Update README

Signed-off-by: Priya Wadhwa <priya@chainguard.dev>

Signed-off-by: Priya Wadhwa <priya@chainguard.dev>

Add CHANGELOG.md for v1.0.0-rc.1 (sigstore#1110)

Signed-off-by: Priya Wadhwa <priya@chainguard.dev>

Signed-off-by: Priya Wadhwa <priya@chainguard.dev>

Cut 1.0 prerelease (sigstore#1105)

Signed-off-by: Priya Wadhwa <priya@chainguard.dev>

Signed-off-by: Priya Wadhwa <priya@chainguard.dev>

Update CHANGELOG.md for 0.12.2 release

Signed-off-by: Priya Wadhwa <priya@chainguard.dev>