Add lido-exporter alert rules and alertmanager for monitoring stack

[khalifaa55]

Changes:

• Include lido-exporter alerts for penalties and exit requests metrics.
• Include Prometheus alertmanager to Prometheus and Grafana
• Add Grafana OnCall plugin to Grafana

Types of changes

What types of changes does your code introduce?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Other (please describe):

Testing

Requires testing

• Yes
• No

In case you checked yes, did you write tests?

• Yes
• No

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 55.12821% with 35 lines in your changes missing coverage. Please review.

Project coverage is 44.78%. Comparing base (d7968c3) to head (00be8cd).

Files with missing lines	Patch %	Lines
internal/monitoring/services/prometheus/service.go	47.82%	12 Missing and 12 partials ⚠️
internal/monitoring/monitoring.go	65.62%	6 Missing and 5 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #425      +/-   ##
===========================================
+ Coverage    44.70%   44.78%   +0.08%     
===========================================
  Files          115      115              
  Lines         9994    10056      +62     
===========================================
+ Hits          4468     4504      +36     
- Misses        5033     5046      +13     
- Partials       493      506      +13     

Flag	Coverage Δ
unittests	44.78% <55.12%> (+0.08%)	⬆️

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