fix: Append state.dir directive to ksql-server.properties

[andrewegel]

• Moved RPM scriptlet that appends state.dir to %post
• Appended newline to config/ksql-server.properties so the append above
  doesn't wind up on the same line as another directive

Description

The debian packages' /etc/ksqldb/ksql-server.properties had this line incorrectly appended

# ksql.schema.registry.url=http://localhost:8081state.dir=/var/lib/kafka-streams

TO remedy that, I added an extra newline to config/ksql-server.properties where I believe this file is sourced from.

And the RPMs /etc/ksqldb/ksql-server.properties didn't have this at all. RPM didn't because the script (that I moved) Was running before the package was even installed, so the file -f check failed. I moved this check to %post so that the check/append occurs when the package & file are actually installed.

Testing done

Non-code change. Nightly builds will pick this change up where we can verify the change is present in the OS packages.

Reviewer checklist

• Ensure docs are updated if necessary. (eg. if a user visible feature is being added or changed).
• Ensure relevant issues are linked (description should include text like "Fixes #")

[andrewegel]

@confluentinc/ksql this is still pending review from one of you - minor change.

[spena]

lgtm