Add OpenCLI integration to Spectre.Console.Cli

[patriksvensson]

• I have read the Contribution Guidelines
• A maintainer has signed off on the changes and the issue was assigned to me
• All newly added code is adequately covered by tests
• All existing tests are still running without errors
• The documentation was modified to reflect the changes OR no documentation changes are required.

Changes

Added OpenCLI integration to Spectre.Console.Cli

Usage

Add the --help-dump-opencli option to your application, and an
OpenCLI description will be written to stdout.

$ ./myapp --help-dump-opencli

If you want to save it to disk, pipe it to a file.

$ ./myapp --help-dump-opencli > myapp.openapi.json

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Please upvote 👍 this pull request if you are interested in it.

[FrediKats]

Thx, @patriksvensson <3

Waiting for release with this new feature.

[patriksvensson]

Will try making a new release today (probably tonight)