feat(extension-api): Allows to select a file for string properties

[benoitf]

What does this PR do?

provides a file selector if formatter is set to file on string properties in properties

Screenshot/screencast of this PR

tFpBbQl4Dm.mp4

What issues does this PR fix or reference?

#185

How to test this PR?

Add in package.json of for example podman extension a new property like

        "podman.factory.machine.image-path": {
          "type": "string",
          "format": "file",
          "scope": "ContainerProviderConnectionFactory",
          "description": "Image Path (Optional)"
        }

then in settings/resources/podman, when creating a podman machine you should see a new field where you can select a file

Change-Id: Ibb5a069be31e47ccf68c9c5654478a7861e8ec89
Signed-off-by: Florent Benoit fbenoit@redhat.com

[cdrage]

Tested and LGTM!

[slemeur]

Nice! 👍