* Alerting: implement loki query for alert state history
* extract selector building
* add unit tests for selector creation
* backup
* give selectors their own type
* build dataframe
* add some tests
* small changes after manual testing
* use struct client
* golint
* more golint
* Make RuleUID optional for Loki implementation
* Drop initial assumption that we only have one series
* Pare down to three columns, fix timestamp overflows, improve failure cases in loki responses
* Embed structred log lines in the dataframe as objects rather than json strings
* Include state history label filter
* Remove dead code
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Co-authored-by: Alex Weaver <weaver.alex.d@gmail.com>
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