refactor(auth): Persist the SECRET_KEY

[mehaase]

During development, every time you save a source file it reloads the
Django server which generates a new SECRET_KEY which means you have to
log in again, which is extremely tedious. This commit saves the
generated key to the data directory so that it can be reused.

Also modified code coverage to exclude settings.py and migrations.

[codecov]

Codecov Report

Merging #154 (3317fa9) into master (b5bf8a8) will increase coverage by 1.23%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #154      +/-   ##
==========================================
+ Coverage   94.35%   95.58%   +1.23%     
==========================================
  Files          20        8      -12     
  Lines         850      748     -102     
==========================================
- Hits          802      715      -87     
+ Misses         48       33      -15     

Impacted Files	Coverage Δ
src/tram/tram/settings.py
...rc/tram/tram/migrations/0006_auto_20210618_1426.py
...igrations/0003_documentprocessingjob_created_by.py
...rc/tram/tram/migrations/0004_auto_20210429_1053.py
src/tram/tram/migrations/0001_initial.py
src/tram/tram/migrations/0008_attackgroup.py
...rc/tram/tram/migrations/0009_auto_20211209_1703.py
...rc/tram/tram/migrations/0005_auto_20210429_1246.py
...rc/tram/tram/migrations/0010_auto_20211209_1708.py
src/tram/manage.py
... and 2 more

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[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication