#### What type of PR is this?
/kind cleanup
/area core
#### What this PR does / why we need it:
Update Halo version to 2.4.0-SNAPSHOT for next development.
#### Does this PR introduce a user-facing change?
```release-note
None
```
#### What type of PR is this?
/kind cleanup
/area core
#### What this PR does / why we need it:
Bump Halo version to 2.3.0-SNAPSHOT and update README.md
#### Does this PR introduce a user-facing change?
```release-note
None
```
#### What type of PR is this?
/kind cleanup
/area core
#### What this PR does / why we need it:
Bump version to 2.2.0-SNAPSHOT for next iteration.
#### Does this PR introduce a user-facing change?
```release-note
None
```
#### What type of PR is this?
/kind improvement
/area core
#### What this PR does / why we need it:
Bump halo version to 2.1.0-SNAPSHOT for next release.
#### Which issue(s) this PR fixes:
```release-note
None
```
#### What type of PR is this?
/kind improvement
/area core
#### What this PR does / why we need it:
Bump Halo version in gradle.properties for next release.
#### Does this PR introduce a user-facing change?
```release-note
None
```