fix: retain autostart setting (#4647)

[lstocchi]

What does this PR do?

This PR cleans the code that defines the autostart setting and fixes a problem when storing its value.

Screenshot/screencast of this PR

N/A

What issues does this PR fix or reference?

it fixes #4647

How to test this PR?

1. check that the autostart setting is actually saved
2. set autostart, stop machine, restart podman desktop, check that the autostart setting is true and the podman machine is started
3. set autostart to false, stop machine, restart desktop, check autostart setting is false and the podman machine is still stopped.

[benoitf]

I have a question, I see lot of people still using old versions

here it looks like if we remove all properties, users migrating from an old version will have their autostart setting being ignored ?

[lstocchi]

@benoitf ppl that uses the old version will end up to a true value.
Having both complicates the code and we agreed on moving on specific provider autostart setting.
As the autostart is not working as expected i think it's a good time to remove old code and start from 0 again. The worst scenario is that people will see the autostart setting enabled if they set it to false using the old version, but we can say there was a bug and it was fixed. If you disable it again, it will work fine.

[jeffmaury]

LGTM