ref(escalating-issues): Move functions to centralize helper functions

[jangjodi]

Move escalating issue forecast helper functions into centralized location

Move save_forecast_per_group and get_forecasts to src/sentry/issues/forecasts.py
Move parse_groups_past_counts to src/sentry/issues/escalating.py since it is related to the snuba query

[codecov]

Codecov Report

Merging #47586 (3eb6a44) into master (249acba) will increase coverage by 0.14%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #47586      +/-   ##
==========================================
+ Coverage   80.60%   80.74%   +0.14%     
==========================================
  Files        4762     4763       +1     
  Lines      201390   201395       +5     
  Branches    11618    11618              
==========================================
+ Hits       162332   162623     +291     
+ Misses      38802    38516     -286     
  Partials      256      256              

Impacted Files	Coverage Δ
src/sentry/issues/escalating.py	100.00% <100.00%> (ø)
src/sentry/issues/forecasts.py	100.00% <100.00%> (ø)
src/sentry/tasks/weekly_escalating_forecast.py	95.23% <100.00%> (-2.59%)	⬇️

... and 35 files with indirect coverage changes

[armenzg]

Good call on the forecasts.py module!