feat: Improve registry validation, error if unknown variables are used

[cszatmary]

When reading a registry, detailed validation errors are recorded and reported. Instead of simply aborting after the first error, validation/parsing of a registry will continue if the error is not critical (ex: failing to read the file is will cause it to abort like before). This allows all the errors in a registry to be reported at once, allowing users to identify and fix all the issues instead of one at a time.

Additionally:

• tb registry validate has received a complete overhaul. The majority of this was thanks to the changes mentioned above. By using the detailed errors returned, a much better output is generated for the user.
• tb registry validate has a --strict flag which will error if unknown variables are encountered in a services.yml file. Currently, unknown variables were silently ignored and replaced with "". This was an unintended bug, which caused issues as tb would not report any errors, but then services would not behave as expected. However, changing this now would technically be a breaking change. As a result this solution has been designed in a non-breaking way. Users can opt into detecting unknown variables, but it will not be forced by default. In the future if we do a breaking change we could make this required.

tb registry validate before

tb registry validate after

[ohsabry]

good shit dude