[WIP] adding a new workflow to validate the FlexibleIPAM feature

[KMAnju-2021]

#6887

[rajnkamr]

Use GitHub Actions caching to avoid re-downloading tools like Kind in every run, which can save build time

[rajnkamr]

- name: Validate Antrea image file
  run: |
    if [ ! -f antrea-ubuntu.tar ]; then
      echo "Error: antrea-ubuntu.tar not found. Ensure the image artifact was downloaded correctly."
      exit 1
    fi

[rajnkamr]

Mention specific disk space needed to run ipam tests in cncf runners

- name: Verify sufficient disk space
  run: |
    AVAILABLE_SPACE=$(df --output=avail / | tail -n1)
    if [ "$AVAILABLE_SPACE" -lt 5000000 ]; then 
      echo "Insufficient disk space for the tests."
      exit 1
    fi

[antoninbas]

The title of the PR is misleading: we are adding a new workflow to validate the FlexibleIPAM feature. The fact that we use a non-default runner is an "implementation detail".

[antoninbas]

I would remove this step, unless you know that there is a shortage of disk space on these runners