Expose async client

[jon23d]

Is there an existing issue for this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe.

I am running an async codebase, and alpaca-py is blocking

Describe the solution you'd like.

Either expose an async client (httpx is great), or add to the documentation a discussion of the concept (for example, workarounds, thread-safety, etc).

Describe an alternate solution.

No response

Anything else? (Additional Context)

Y'all are doing great work. Thanks!