Configure Splunk Launch explicitly to prevent future clobbering

[arcsector]

Summary

This PR is needed because of the changes Splunk introduced in v9.1.0 of the UF, which changed the default username of the Splunk UF installation to splunkfwd from splunk. This raised awareness of the fact that we can't rely on Splunk to keep its own internal values consistent, and as such explicitly specifying the user and service name will help prevent these values from being changed in the future.

This PR also adds in additional functionality for those who would like to store their indexes in a different location. A use case for this would be if you want to run your indexes on slower SSDs than your main application, you would set SPLUNK_HOME to be on your root FS and then have your SPLUNK_DB pointing to your other mounted SSDs like at /data/splunk/db. This was done as it seemed like the right place to put this type of feature.

Added:

• Splunk launch config setting Splunk user, home, service name, and DB path if defined
• New var for DB Path

Changed:

• README references new Splunk launch task
• installation task includes Splunk launch task