functionapp: ARR Affinity and plan descruction

**Describe the bug**
When using az cli to deploy a web app I am able to configure ARR Affinity using the following:
`az webapp update --client-affinity-enabled.`

When trying to configure the same for functionapp there is no such command.

When I delete the functionapp to try recreating from scratch, it deletes the app plan because unlike webapp commands there is also no option to keep-empty-plan

**To Reproduce**
Deploy a functionapp using the following:
`az functionapp create --name --resource-group --plan --storage-account `

Attempt to update the ARR Affinity using a similar command like
`az functionapp update --client-affinity-enabled`

Delete the functionapp
`az functionapp create --name --resource-group `

Recreate the plan so you are ready to recreate the functionapp again

**Expected behavior**
I would expect the command would update the setting since it's the same setting and visible in the portal the same as web apps.

**Environment summary**
I'm running the latest version of az cli locally on my system