limactl: start: introduce --set <stringArray> flag to pin static config values instead of creating custom config file

[Dentrax]

Description

Since limactl already supports passing custom configuration files, sometimes it decreases the overall UX. It enforces us to create custom config files each time even we want to set just a single variable, such as localPort. Here is an example use-case:

So that we can also override the values in a file by using the '--set' flag and pass configuration from the command line as follows:

$ limactl start foo -f my_defauly.yaml --set ssh.localPort=15555 --set arch=x86_64

We can specify the --set flag multiple times. The priority will be given to the last (right-most) set specified.

--set stringArray:

set values on the command line (can specify multiple or separate values with commas: key1=val1,key2=val2)

/cc @developer-guy

[AkihiroSuda]

This has been on plan, and will be implemented after merging #1069

[AkihiroSuda]

See also #971 (comment)