DictConfig: Support float and bool keys

[Jasha10]

Currently we have DictKeyType = Union[str, int, Enum], i.e. DictConfig supports keys of type str or int or Enum.

This feature request is for expansion of DictKeyType to include float and bool:
DictKeyType = Union[str, int, Enum, float, bool].

Additionally, given that null is a valid as a key in YAML, we could consider adding support for None as a DictConfig key, although I suspect that support for None may be more difficult than support for float/bool.

As a starting point for implementation, PR #454 implemented support for int key type in DictConfig.

[omry]

Thanks for filing @Jasha10.
I will welcome a diff from you adding support for those two types as keys but currently there are higher priority things to work so this is not planned for the next release of OmegaConf (unless you or someone else sends a soid PR to add it).