[s3inbox] run healthchecks in main process

[MalinAhlberg]

Related issue(s) and PR(s)
This PR addresses #992.

Description

• The /health endpoint is put on the same port as s3inbox (ie. is run on the server started in s3inbox.go).
• Also a HEAD request to s3inbox will return the health status.
• If there are problems with the connection to MQ or DB while checking the health, CheckHealth attempts to restore it.
• Go tests updated
• Integration tests added
• The /ready and /live endpoints are removed
• The /healthz enpoint (provided by the charts) is removed

If this is to be continue: create issues for updating charts etc reflect this change.

How to test
curl 'localhost:18000' -H 'Authorization: Bearer $token' -I
curl 'localhost:18000/health' -H 'Authorization: Bearer $token'

[jbygdell]

You're on the right path.
But the healcheck functions needs to be inside the proxy struct so it can issue reconnect/recreate if the MQ or DB connections go down. Look in the checkAndSendMessage function and see an example.

[MalinAhlberg]

Thanks for the quick review @jbygdell! Fixes are pushed.

[nanjiangshu]

Great work! I left a minor comment regarding the use of GET request and HEAD request for obtaining the HTTP code. But I approve it anyway 😄