feat: add basic deployment lock implementation

[shini4i]

When merged, it will close #251

Currently, the implementation is highly experimental and does not cover cases when the application was started after the start of the pre-defined window for deployment lock.

We can pass the schedule configuration from helm values like this: (the required changes are not yet merged)

lockdownSchedule:
  - cron: "* 2 * * *"
    duration: "3h45m"

Or just set it from the web interface. In case of keycloak integration being enabled, membership in a privileged group is required.

An alternative approach would be to create some custom way to pass the lockdown timeframe and validate each request against it. At the moment, it seems to be overengineering.

[codecov]

Codecov Report

Attention: Patch coverage is 37.32394% with 89 lines in your changes are missing coverage. Please review.

Project coverage is 51.85%. Comparing base (78e6d1b) to head (4fc990d).

Files	Patch %	Lines
cmd/argo-watcher/server/router.go	33.66%	62 Missing and 5 partials ⚠️
cmd/argo-watcher/server/cron.go	38.46%	16 Missing ⚠️
cmd/argo-watcher/config/parsers.go	57.14%	2 Missing and 1 partial ⚠️
cmd/argo-watcher/server/server.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #252      +/-   ##
==========================================
- Coverage   53.42%   51.85%   -1.57%     
==========================================
  Files          20       22       +2     
  Lines        1402     1537     +135     
==========================================
+ Hits          749      797      +48     
- Misses        586      667      +81     
- Partials       67       73       +6     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[sonarcloud]

Quality Gate passed

Issues
0 New issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud