Provide ability to tag queries in Query Analytics

It would be great to be able to assign pre-generated as well as arbitrary tags to queries in Query Analytics. The point is to be able to quickly analyze a group of queries for review / sharing to colleagues when performing triage of a system.

• Could then choose to view by selected tags, or exclude selected tags

• Pre-generated would be those executed by pmm-agent, Custom Queries

• Need to be able to be assigned by Custom Queries (each query should have a similar tag like mysql_custom_query as well as ability to add an arbitrary tag unique to the environment i.e. service_web_frontend_42 )

• Additional "Queries to be reviewed" vs "Already Reviewed" so that setting up a query review process is simple, you don't need to look at certain queries you know have already been tuned and examined (PCT model)

• Should be accessible via API so then programmatically an environment can be configured to tag queries based on digest