Support Kira's Clocks

[NiklasEi]

See https://tesselode.github.io/kira/clocks.html

[james-j-obrien]

I need to leverage clocks for my use case. I had started manually depending on kira directly in order to gain access to them but it would be great to have it upstreamed rather than duplicating that effort.

Would you be open to discussing how these would ideally be integrated to bevy_kira_audio so that I could start implementing a PR with clock support? Otherwise I'll just do my own implementation locally

[james-j-obrien]

I have a fork that has basic, quick and dirty support here: https://github.com/james-j-obrien/bevy_kira_audio Missing docs and dynamic clock support but appears to work as expected.