migration: add columns for hashed values on ApiToken

[mdtro]

In support of our improved API tokens initiative (getsentry/rfcs#32), this PR adds two null-able columns to the ApiToken model that will hold the hash values.

Hashed values for token values will be implemented over several PRs to maintain backwards compatibility and to prevent broken state between versions.

[github-actions]

This PR has a migration; here is the generated SQL for src/sentry/migrations/0647_apitoken_add_hashed_columns.py ()

--
-- Add field hashed_refresh_token to apitoken
--
ALTER TABLE "sentry_apitoken" ADD COLUMN "hashed_refresh_token" varchar(128) NULL;
--
-- Add field hashed_token to apitoken
--
ALTER TABLE "sentry_apitoken" ADD COLUMN "hashed_token" varchar(128) NULL;

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6809aed) 81.47% compared to head (f888338) 81.46%.
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #65300      +/-   ##
==========================================
- Coverage   81.47%   81.46%   -0.01%     
==========================================
  Files        5255     5255              
  Lines      232091   232093       +2     
  Branches    45521    45521              
==========================================
- Hits       189087   189086       -1     
- Misses      37124    37126       +2     
- Partials     5880     5881       +1     

Files	Coverage Δ
src/sentry/backup/comparators.py	95.26% <ø> (ø)
src/sentry/models/apitoken.py	99.06% <100.00%> (+0.01%)	⬆️

... and 11 files with indirect coverage changes

[wedamija]

lgtm, I think you just need to follow this instructions in that test failure to update snapshots