Support for special tunable values outside of the range

[motus]

Enables special values outside of the range (e.g., -1 with a range of [0, 100]).

To do we make use of "conditionals" in ConfigSpace to constrain the space. This has a number of implementation implications, addressed below:

• Add support for special values to the Tunable class
• Add unit tests for assigning special values outside of the range to the Tunable objects
• Add special values outside of the range to the unit tests for ConfigSpace conversion
• Implement proper TunableGroups to ConfigSpace conversion for tunables with special values
• Update mlos_core optimizers to support conditionals and special values in ConfigSpace
• Add more unit tests to check the conversion
• Make LlamaTune adapter support conditionals in ConfigSpace

[bpkroth]

A few nits here and there, but I think the main thing we should revisit is whether to support mixed numerical and string types for special values.

[bpkroth]

LGTM

I left one place to add a comment that probably needs some pylint checks for spacing.

I think one tweak we/I could add in a future PR would be to update the json schemas to account for disallowing ! characters in the names, but that doesn't have to be here.