add support for float pointer values for references

[eljohnson92]

Description of your changes

This change allows for types of references that are not strings. some terraform providers use "number" types for resource IDs which seem to get translated to float64 as part of upjet. when trying to use them as references previously only strings were supported, this PR along with a PR #367 in crossplane-runtime allows for "number" IDs to also be supported as references Fixes #

I have:

• [x] Read and followed Crossplane's [contribution process].
• [x] Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

This has been tested by the linode-provider, which is using my forked version of this repo and the crossplane-runtime repo

[turkenh]

@eljohnson92 linter is failing, could you check and fix it?

[eljohnson92]

@turkenh I did a small refactor to fix the cyclomatic complexity in that function and bring it back below 10. should be good for another review