Merge pull request grpc#20348 from veblush/v1.24.0-bump

Bump version to 1.24.0

Merge pull request grpc#20257 from muxi/v1.24.x

Fix v1.24.0-pre1 objc release

Regenerate projects

Merge pull request grpc#19952 from karthikravis/v1.22.x

Bump version to v1.22.1

Merge pull request grpc#19950 from karthikravis/v1.23.x

Bump version to v1.23.0

Merge pull request grpc#19828 from karthikravis/v1.23.x

Bump version to v1.23.0-pre1

Merge pull request grpc#19528 from veblush/v1.22.x

Bump version v1.22.0

Merge pull request grpc#19415 from apolcyn/backport_skip_broken_distrib

Backport "Skip all ruby distrib tests that use ruby 2.2" to 1.22.x

Merge pull request grpc#19283 from stanley-cheung/bump-to-1_21_4

Bump to version v1.21.4

Merge pull request grpc#19281 from stanley-cheung/bump-to-1_21_4_pre1

Bump to version v1.21.4-pre1