[Liqoctl] Specify other (non-standard) resources with liqoctl commands

[claudiolor]

Description

This PR introduces the --resource flag to the peer create virtualnode and create resourceslice commands, to allow the user to
directly specify custom resources without the needs to manually edit the manifests.

E.g.

liqoctl peer --remote-kubeconfig $MY_KUBECONFIG \
  --cpu 10 \
  --memory 20Gi \
  --resource nvidia.com/gpu 2

or

liqoctl create resourceslice my-slice --remote-cluster-id remote-cluster-id \
  --cpu 4 \
  --memory 8Gi \
  --pods 30 \
  --resource nvidia.com/gpu=2`

The resource flag can be repeated as many times as the number of non-standard resources to ask the provider cluster for:

liqoctl peer ... --resource nvidia.com/gpu=2 --resource custom.my/resource=2Gi

[adamjensenbot]

Hi @claudiolor. Thanks for your PR!

I am @adamjensenbot.
You can interact with me issuing a slash command in the first line of a comment.
Currently, I understand the following commands:

• /rebase: Rebase this PR onto the master branch (You can add the option test=true to launch the tests
  when the rebase operation is completed)
• /merge: Merge this PR into the master branch
• /build Build Liqo components
• /test Launch the E2E and Unit tests
• /hold, /unhold Add/remove the hold label to prevent merging with /merge

Make sure this PR appears in the liqo changelog, adding one of the following labels:

• feat: 🚀 New Feature
• fix: 🐛 Bug Fix
• refactor: 🧹 Code Refactoring
• docs: 📝 Documentation
• style: 💄 Code Style
• perf: 🐎 Performance Improvement
• test: ✅ Tests
• chore: 🚚 Dependencies Management
• build: 📦 Builds Management
• ci: 👷 CI/CD
• revert: ⏪ Reverts Previous Changes