feat: generate SBOMs for container images on release

[mowies]

This PR

• generates SBOMs for all 3 container images upon release
• the SBOMs are attached to the newly created release in JSON format

Fixes #300

[codecov]

Codecov Report

Merging #571 (5489e86) into main (9516fcf) will decrease coverage by 0.10%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #571      +/-   ##
==========================================
- Coverage   49.92%   49.81%   -0.11%     
==========================================
  Files          60       60              
  Lines        5528     5528              
==========================================
- Hits         2760     2754       -6     
- Misses       2661     2665       +4     
- Partials      107      109       +2     

Impacted Files	Coverage Δ
...ptnworkloadinstance/reconcile_prepostdeployment.go	81.81% <0.00%> (-9.10%)	⬇️
...or/controllers/keptnworkloadinstance/controller.go	77.04% <0.00%> (-1.54%)	⬇️

Flag	Coverage Δ
component-tests	50.58% <ø> (+0.94%)	⬆️
keptn-lifecycle-operator	47.85% <ø> (ø)
scheduler	21.17% <ø> (ø)

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[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
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No Coverage information
No Duplication information

[thschue]

lgtm