Feat(eos_cli_config_gen): Support for "agents" config

[gmuloc]

Change Summary

Render stuff like:

agent BLAH environment BLAH=BLAH
agent KernelFib environment TOTO=TEAH

Component(s) name

arista.avd.eos_cli_config_gen

Proposed changes

ceos2(config)#show cli commands | grep agent
[no|default] agent AGENT environment ENVIRON_CONFIG
[no|default] agent AGENT memory allocations heap fastbin limit SIZE
[no|default] agent AGENT shutdown [ supervisor ( active | standby | all ) ]
[no|default] agent AGENT_NAME warm-restart ( ( allowed ALLOWED_NUM ) | ( window WINDOW_NUM ) | always )
agent fatal-error action ACTION

ceos2(config)#agent BLAH environment ?
  EXPR  Agent environment configuration in the form of VAR1=VAL1:VAR2=VAL2:...

    agents:
      - name: <str>
        environments:
          - name: <str>
            value: <str>

How to test

molecule

Checklist

Repository Checklist

• My code has been rebased from devel before I start
• I have read the CONTRIBUTING document.
• My change requires a change to the documentation and documentation have been updated accordingly.
• I have updated molecule CI testing accordingly. (check the box if not applicable)

[carlbuchmann]

Need to update eos_cli_config_gen input-variable.md

[carlbuchmann]

LGTM