Example basic lambda service with external/multiple runtimes

[heavens]

Apologies in advance if this topic has already been addressed and or is out of scope for what may be accepted as an example. A topic I've noticed being broughtup periodically is the ability to use the lambda_runtime with a custom runtime/executor instead of the one currently baked in. In light of this, I drafted a minimal example showcasing how an application that has a lambda microservice could look. I kept the implementation minimal serving as more of a proof of concept to guide users however, if required, a more in-depth example could be drafted up.

Issue #, if available:

Description of changes: This example is a fork of the current basic lambda example with the additions of running a lambda microservice within a mock application that also runs another theoretical service utilizing channels to pass messages across threads.

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[calavera]

someone might find it useful 👍