Add prefix in the query

[fyang13]

What happened:

Can the plugin be updated with "/** Grafana initiated search */" prefix to the query just like the original humio plugin here?
It would be very helpful to allow LogScale admin to report on query requests submitted through Grafana LogScale datasource plugin vs. from native query nodes.
This was originally requested via: #311

What you expected to happen:
User should be aware if backend report back the query result with warning.

How to reproduce it (as minimally and precisely as possible):

Screenshots

Anything else we need to know?:

Environment:

• Grafana version:
• Plugin version:
• OS Grafana is installed on:
• User OS & Browser:
• Others: