Build improvements and paying down related tech debt

[cbrit]

Lots going on here, I recommend reviewing one commit at a time. This PR will

• Fix build caching in CI to speed up builds and combine format, linting, building, and testing into one job. Second part is debatable. Felt weird having a bunch of repeated caching code for the separate jobs.
• Remove the workspace and various ABI/proto build/bindings crates in favor of using build.rs to build ABI and proto bindings. The generation runs before each build and drops the bindings directly into the steward crate. This could be improved by doing some sort of checksum to avoid unnecessary re-generation which can slow down builds by a few seconds (probably more in CI).
• Move the contents of steward/ into the root of the repository as a consequence of the above
• Reduce docker image size a lot by copying the final binary to a vanilla debian image (the same base image/version as the rust image used). Worth noting that a consequence of the change to use build.rs for proto bindings is that the version of tonic-build we are using requires rustfmt to be installed by default.
• Speed up API doc build which now outputs a single markdown file
• Build Go protos and API docs in the build.rs script

Other tidying:

• Move scripts into a scripts folder

Closes #184, closes #188

Note: The API docs now build to a single markdown file. If we want adaptors to be neatly separated we'll need put them in their own sub-package.

[cbrit]

Moved to draft as there are some things that need tweaking

[EricBolten]

Will review pending merge conflict resolution.

[EricBolten]

It also appears the steward-build action was broken in this changeset, building the go protos is panicking.