Upstreaming of `bevy_kira_audio`.

## What problem does this solve or what need does it fill?

The current `bevy_audio` is quite bare-bones, and `bevy_kira_audio` would add a lot of new flexibility / features.

## What solution would you like?

Upstreaming `bevy_kira_audio` into bevy, after making sure the APIs are similar enough.

## What alternative(s) have you considered?

-

## Additional context

I am a relatively new contributer, and have discussed this on discord in `#audio-dev`.

Start by comparing the existing bevy_audio API with bevy_kira_audio and review the prior discussion in Discord's #audio-dev channel. Define the API compatibility work and feature scope before attempting the upstreaming; done means the APIs are sufficiently similar and the integration is accepted into Bevy.

Written by the indexing model from the issue text.