Implement clean install from sources every time

[larsvilhuber]

This should be doable given the work by @ledwindra but needs to be integrated here.

Should connect to #10 to be triggered only when the existing image identifies that an update is available.

Requires that I use the API token to upload to DockerHub.

[larsvilhuber]

Implementation details:

• install Stata in cloud instance (new) (may not need to run the license creation part, TBD)
• run "capture" script
• run "build" script
• run "push" script (new: with DockerHub API token; new new: push to GHC repository as well for cheaper GHA pulls)

[larsvilhuber]

To be clear:

• (a) installing Stata using the official installer requires a license + login credentials to access
• (b) using an existing (bootstrapped) Stata tarball STILL requires a license to update the installed copy, so that it can then be "captured"

[larsvilhuber]

@michaelstepner notes that this may no longer work, so caching the installers somewhere may be necessary.