feat: add CLI debugging commands

[alexmt]

PR add set of CLI commands that simplify configuring notification controller:

• get configured triggers/template

argocd-notifications tools trigger get
argocd-notifications tools trigger get --name on-sync-failed
argocd-notifications tools template get

• eval trigger condition

argocd-notifications tools trigger run 
  on-sync-failed  \         #trigger name
  guestbook                 #app name ( or local app file path )

• print notification to console

argocd-notifications tools template notify \
  app-sync-succeeded  \     #template name
  guestbook                 #app name ( or local app file path )

• send the notification to the specified recipient

argocd-notifications tools template notify \
  app-sync-succeeded  \     #template name
  guestbook \               #app name ( or local app file path ) 
  --recipient slack:argocd-notifications

All commands have --config-map and --secret flags to use local config map, secret files instead of real config map/secret

Progress:

• implementation
• tests
• documentation

[codecov]

Codecov Report

Merging #81 into master will decrease coverage by 1.78%.
The diff coverage is 45.94%.

@@            Coverage Diff             @@
##           master      #81      +/-   ##
==========================================
- Coverage   55.45%   53.66%   -1.79%     
==========================================
  Files          20       24       +4     
  Lines         990     1295     +305     
==========================================
+ Hits          549      695     +146     
- Misses        361      497     +136     
- Partials       80      103      +23     

Impacted Files	Coverage Δ
cmd/bot.go	0.00% <0.00%> (ø)
cmd/main.go	0.00% <0.00%> (ø)
notifiers/notifiers.go	0.00% <ø> (ø)
shared/settings/settings.go	58.90% <0.00%> (-13.98%)	⬇️
cmd/tools/context.go	19.04% <19.04%> (ø)
cmd/tools/tools.go	36.95% <36.95%> (ø)
cmd/controller.go	31.37% <50.00%> (-1.39%)	⬇️
cmd/tools/trigger.go	56.52% <56.52%> (ø)
cmd/tools/template.go	62.72% <62.72%> (ø)
notifiers/webhook.go	71.05% <100.00%> (+1.60%)	⬆️
... and 4 more

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