feat(explore): updates explore saved query serializer param to be an array

[edwardgou-sentry]

Adds a new inner QuerySerializer to contain fields, orderby, groupby, query, visualize, and mode params.
Updates query in ExploreSavedQuerySerializer to now be a list of QuerySerializer.

This change is to provide support for saving Explore Multi Query views. Multiple queries in a Multi Query view is represented through multiple QuerySerializer entries. Single Explore Query views will be saved using a list with a single QuerySerializer element.

A migration isn't necessary for this change, because no changes were made to the model. Also, because the query attribute in the ExploreSavedQuery is already a JSONField, which supports storing lists.

ie the query column before:

{"query":"span.op:[pageload,navigation]","fields":["span.op","timestamp"],"orderby":"-timestamp","visualize":[{"chartType":1,"yAxes":["count(span.duration)"]}],"mode":"samples",...}

the query column after:

{"query":[{"query":"span.op:[pageload,navigation]","fields":["span.op","timestamp"],"orderby":"-timestamp","groupby":["span.op"],"visualize":[{"chartType":1,"yAxes":["avg(span.duration)"]}],"mode":"samples"}],...}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

✅ All tests successful. No failed tests found.

Additional details and impacted files

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##           master   #87503       +/-   ##
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+ Coverage   45.07%   87.74%   +42.66%     
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  Files        9881     9899       +18     
  Lines      560636   561440      +804     
  Branches    22139    22119       -20     
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+ Hits       252714   492640   +239926     
+ Misses     307520    68396   -239124     
- Partials      402      404        +2