editflags: support multiple --set flags instead of ignoring all but the last such parameter

[AndiDog]

I wanted to use lima-based development instructions (from the Kubernetes CAPI project docs):

limactl start template://docker-rootful --name "docker" --tty=false \
  --set '.provision += {"mode":"system","script":"#!/bin/bash\nset -eux -o pipefail\ncat << EOF > \"/etc/sysctl.d/99-capi.conf\"\nfs.inotify.max_user_watches = 1048576\nfs.inotify.max_user_instances = 8192\nEOF\nsysctl -p \"/etc/sysctl.d/99-capi.conf\""}' \
  --set '.mounts[0] = {"location": "~", "writable": true}' \
  --memory 12 --cpus 10 --disk 64 \
  --vm-type vz --rosetta=true

and it turned out that the sysctl settings that are supposed to be applied in the first --set argument are totally ignored without warning because that's how command line parsers usually work. Users should definitely be able to specify this multiple times, so I added support for that.

[jandubois]

Thank you for noticing this! I had assumed that this already worked, but indeed it didn't.

There are already several other options that can be specified multiple times: --dns, --mount, --mount-only, --network. They all build a single expression in their exprFunc.

So I would like to either --set do the same, or to modify all the existing implementations to return a []string as well, for consistency.

You should only change the existing implementation if it simplifies the code. Otherwise --set should just join the individual values together itself and return a single string.

[AkihiroSuda]

I thought we had a similar PR in the past but can't find it