feat(insights): add has_insights_xx span project flags

[KevinL10]

Adds has_insights_xx flags for each insight module to track whether a project has sent spans for that insight module.

These flags are used to determine whether to show the empty state screen when the user visits an insight module. Our current approach involves scanning through the past 90 days of metrics data to check for any matching spans, which is extremely inefficient.

With these new project flags, we can avoid a table scan and improve insight module page load times by 2-3 seconds.

[github-actions]

This PR has a migration; here is the generated SQL for src/sentry/migrations/0731_add_insight_project_flags.py ()

--
-- Alter field flags on project
--
-- (no-op)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.05%. Comparing base (0799003) to head (339147e).
Report is 14 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #72904      +/-   ##
==========================================
+ Coverage   73.27%   78.05%   +4.77%     
==========================================
  Files        6602     6605       +3     
  Lines      294288   294469     +181     
  Branches    50729    50759      +30     
==========================================
+ Hits       215652   229841   +14189     
+ Misses      72050    58293   -13757     
+ Partials     6586     6335     -251     

Files	Coverage Δ
src/sentry/models/project.py	94.62% <100.00%> (+2.11%)	⬆️

... and 849 files with indirect coverage changes