feat: Introduce Postee Actions

[simar7]

This PR introduces Postee Actions, a lightweight (no-code) workflows that allows users to configure Postee to execute ad-hoc but useful post processing steps.

Some use cases include (but are not limited):

1. As a security practitioner, I want to remove a vulnerable image from my node when Trivy scan detects a vulnerability in an image, so that I can keep vulnerable images unavailable for deployment.
2. As a security practitioner, I want to ship Tracee security notifications logs from my node when security events are detected, so that I can build a timelog for forensics purposes.
3. [WIP] As a Kubernetes operator, I want to add labels to my Kubernetes cluster when Starboard detects a vulnerable image in my cluster, so that I can effectively manage vulnerable deployments.

These are some examples of how a user can use Postee Actions.

Signed-off-by: Simar simar@linux.com

[simar7]

@AndreyLevchenko - do you know why the CI is failing?

[codecov]

Codecov Report

Merging #249 (cb50267) into main (ca72375) will increase coverage by 0.46%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #249      +/-   ##
==========================================
+ Coverage   86.87%   87.33%   +0.46%     
==========================================
  Files          28       28              
  Lines        1112     1153      +41     
==========================================
+ Hits          966     1007      +41     
  Misses         88       88              
  Partials       58       58              

Impacted Files	Coverage Δ
router/builders.go	98.01% <100.00%> (+0.96%)	⬆️
router/router.go	86.79% <100.00%> (+0.51%)	⬆️

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