Create Quadlets when there are unsupported keys and values

[TheRealBecks]

It's likely that there will be unsupported keys and values when the compose spec gets a new version or when Podlet does not yet support a already available key or value. That results in issues like #164 and #158

I suggest to introduce another argument that enables Podlet to create Quadlet files even when it does not support all keys and values:

• Use e.g. --ignore-unsupported-keys-and-values
• Internally Podlet creates a map that will add all keys and values that are not supported
• Create Quadlet files out of the supported keys and values like it already does
• Print the not supported map at the end so the user gets feedback of what has not been used for the creation of Quadlet files
  • Printing only works when Podlet is used as a single command on the command line

Benefits:

• There will always be a workaround when Podlet does not support a key or value -> Podlet can always be used to partly generate Quadlet files and therefore life will be easier for the users
• Podlet will not fail in corner cases when the user wants it to succeed

Quadlet files with 90+ % of all features will always be better than 0 % due to unsupported keys and values. Users can manually edit their files afterwards, but they don't have to start from scratch.

[TheRealBecks]

@k9withabone What do you think?

[k9withabone]

In theory, I'm ok with this. Practically, I think it will be very difficult to implement as it would require changing how error handing works across the project. So I think this should go into a "someday-maybe" category of features. The plan is to eventually split the core of Podlet into a library for #20 and error handling will probably be reworked during that effort anyway (more defined error types).