Add Parse Server health check

[dplewis]

New Feature / Enhancement Checklist

• [ ] I am not disclosing a vulnerability.
• [ ] I am not just asking a question.
• [ ] I have searched through existing issues.

Current Limitation

There isn't a convientant way to get ping the /health endpoint on the server

Feature / Enhancement Description

Add Parse.getServerHealth as a quick way to check on the server health without having to make an arbitrary request to a functional endpoint, and without needing keys.

Example Use Case

Useful for server failover.

Alternatives / Workarounds

You can make your own request to the /health endpoint

3rd Party References

SDKs like JS and PHP have it

https://github.com/parse-community/Parse-SDK-JS/pull/1307 https://github.com/parse-community/parse-php-sdk/pull/366