Feat(eos_designs): Enable KERNELFIB_PROGRAM_ALL_ECMP for all wan routers

[ayushmittal-arista]

Change Summary

Enable KERNELFIB_PROGRAM_ALL_ECMP for all wan routers by setting environment variable for KernelFib.

Related Issue(s)

Fixes #

Component(s) name

arista.avd.eos_designs

Proposed changes

Add file agents.py in underlay python_modules to generate agent structured config for KernelFib

 {
     "name": "KernelFib", 
     "environment_variables": [
                {"name": "KERNELFIB_PROGRAM_ALL_ECMP", "value": "1"}
      ]
},

How to test

molecule

Checklist

User Checklist

• N/A

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)

[MaheshGSLAB]

LGTM