Fix(eos_cli_config_gen): update logic in monitor_sessions

[carlbuchmann]

Change Summary

Monitor-session templates expect both keys monitor_session.sources is arista.avd.defined and monitor_session.destinations to be defined before generating any config but this is not required in EOS, so relaxing this check and requirement.

{% if monitor_sessions is arista.avd.defined %}
!
{%     for monitor_session in monitor_sessions | arista.avd.natural_sort('name') if monitor_session.name is arista.avd.defined %}
{%         if monitor_session.sources is arista.avd.defined and monitor_session.destinations is arista.avd.defined %} # <- remove this if condition.

Component(s) name

arista.avd.eos_cli_config_gen

Proposed changes

Update logic and optimize tests in template.
Update indentation.
Updated eos_designs_unit test case where monitor session is configured without destination, and now we see configuration being generated.

How to test

All Molecule tests should pass!

[github-actions]

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[github-actions]

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[github-actions]

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[gmuloc]

As discussed on chat with @ClausHolbechArista, this PR could trigger some changes for existing deployment with only source pr destination that will suddenly start to generate config (hence a "breaking change").

I would be in favor of:
1/ Adding a ! indicating it is breaking (to our output) but it is a bug fix so it is allowed by SemVer
2/ maybe pushing this to 5.0.0 or if we believe we can't wait then making it a patch with an addition in the release notes but we may be argued that we don't follow SemVer stricto sensu

[sugetha24]

LGTM