feat(overviews): Add API overview endpoints for findings and severity

[vicferpoy]

Description

This PR includes the following:

• New linked Celery task for aggregating finding data when a scan is complete.
• New endpoints for finding overviews:
  • GET /overviews/findings
  • GET /overviews/findings_severity

GET /overviews/findings

{
    "data": {
        "type": "findings-overview",
        "id": "n/a",
        "attributes": {
            "new": 0,
            "changed": 0,
            "unchanged": 3541,
            "fail_new": 0,
            "fail_changed": 0,
            "pass_new": 0,
            "pass_changed": 0,
            "muted_new": 0,
            "muted_changed": 0,
            "total": 3541,
            "fail": 1076,
            "muted": 0,
            "pass": 2458
        }
    },
    "meta": {
        "version": "v1"
    }
}

GET /overviews/findings_severity

{
    "data": {
        "type": "findings-severity-overview",
        "id": "n/a",
        "attributes": {
            "critical": 283,
            "high": 1488,
            "medium": 1398,
            "low": 367,
            "informational": 5
        }
    },
    "meta": {
        "version": "v1"
    }
}

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

Attention: Patch coverage is 67.51592% with 51 lines in your changes missing coverage. Please review.

Project coverage is 90.24%. Comparing base (04d99f1) to head (6ece3bb).
Report is 512 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5910      +/-   ##
==========================================
- Coverage   93.69%   90.24%   -3.45%     
==========================================
  Files          58     1205    +1147     
  Lines        4663    40399   +35736     
==========================================
+ Hits         4369    36460   +32091     
- Misses        294     3939    +3645     

Components	Coverage Δ
prowler	89.90% <100.00%> (∅)
api	92.81% <67.51%> (-0.88%)	⬇️