[ch20895] get kotlin codegen working properly

[eonwhite]

With @Rodlikespants, we made a number of changes to update the Kotlin swagger-codegen:

• Added a build-codegen-cli.sh convenience script which builds and copies the jar to ~/dev
• Fixed the output of Lists of Enums (this was breaking previously)
• (We think) fixed the longstanding connection leak https://sentry.io/organizations/charthop/issues/1426893272/ by calling .string() which automatically closes the OkHttp response
• Added response codes to the various Exceptions and added a parent ApiException class for catching them
• Restored two changes which had been manually added into the repo (10-minute timeout for API requests and content-type guessing) https://github.com/charthop/jvm/commit/f01c23ac0054013d6d39366dd6a9e67d9cdbe07a#diff-d9dda1c568cfd44f9b23c12d3e0bc02bceec1ab051b76eed185f8af1cc35f3ab and https://github.com/charthop/jvm/commit/48f9e67cf33ec29aba7e0fef7cd5f0c476dbae5a#
• Removed various warnings

[shortcut-integration]

This pull request has been linked to Clubhouse Story #20895: Get kotlin codegen working properly.