* Moves all manual build steps to make targets, to simplify
the commands run, and reduce chance for error.
* Removes the need to remember to rebuild the builder
image by building it automatically prior to launching.
* Adds a new make target for deploying multiple runtime
versions at once to speed up the common case.
* Reduces repetition/superfluous content in documentation.
* Removes unused `S3_REGION` from `dockerenv.default`
(the contents of S3 buckets inherit the region of the bucket).
* Documents build dependencies in `requirements.txt`.
Closes @W-8119717@.
[skip changelog]
Ed Morley