search: query pings for operators and predicates
Created by: rvantonder
WIP. Adds the following fields for tacking search query metrics to existing search_usage record.
- OperatorAnd
- OperatorNot
- OperatorOr
- RepoContains
- RepoContainsFile
- RepoContainsContent
- RepoContainsCommitAfter
- SelectRepo
- SelectFile
- SelectSymbol
- SelectCommitDiffAdded
- SelectCommitDiffRemoved