ux: improve `cilium install`'s `wait` and `restart-unmanaged-pods` interaction

[nbusseneau]

Context

For cilium install:

• wait defaults to true
• restart-unmanaged-pods to true
• But --restart-unmanaged-pods=true "implies" --wait=true behavior (this is expected because unmanaged pods can only be restarted after Cilium is ready):

https://github.com/cilium/cilium-cli/blob/c6ec394061fe01eeaef27d2d061d8b7b3db0626a/install/install.go#L1685-L1690

Issue

Manually specifying --wait=false has no effect on its own from a code logic standpoint, since restart-unmanaged-pods=true by default. In practice, this means that we always wait for Cilium pods to be ready even if --wait=false is specified, except if also specifying --restart-unmanaged-pods=false.

This is a bit surprising from a UX standpoint, because one could expect manually specifying --wait=false to be "stronger" than the default value of restart-unmanaged-pods.

Proposal

• If specifying --wait=false, imply restart-unmanaged-pods=false and add a warning to the user that unmanaged pods will not be restarted and need to be restarted manually.
• If specifying --restart-unmanaged-pods=false, leave default wait=true and add a warning to the user that unmanaged pods will not be restarted and need to be restarted manually.
• If specifying --wait=false and --restart-unmanaged-pods=true, fail due to flag incompatibility.

I think we can check for these scenarios using https://pkg.go.dev/github.com/spf13/pflag#FlagSet.Changed to know if a flag was changed from the CLI.

Further improvements

• Add a dedicated cilium restart-unmanaged-pods command (find a better name :D) to restart unmanaged pods at will if this was skipped at cilium install time.