implement a basic project toml schema

[webern]

Description

Implement the algorithm by which Twoliter finds Twoliter.toml.
Implement a simple schema which includes:

• The twoliter schema version (required)
• The SDK to use (it is optional for the user to specify this)
• Optional: the version of the Twoliter binary to lock to (it is optional for the user to specify this)

Definition of Done

Done when Twoliter commands demand that Twoliter.toml exist, can find it, and deserialize it.

Depends on:

• twoliter make design #6

id: texec_basic_projtoml
epic: twoliter_exec

Related to bottlerocket-os/bottlerocket#2669