[cli][script] Fix misspelling in cli bootstrapping script

[jimschubert]

Fixes a misspelling in the cache directory environment variable introduced in #3631, warning users that they need to migrate to the properly spelled variable.

Also creates the directory if it doesn't exist.

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[jimschubert]

@RonnyPfannschmidt just an FYI

[jimschubert]

This can be tested with:

OPENAPI_GENERATOR_DOWLOAD_CACHE_DIR="$(pwd)/.bak/dowload" bash bin/utils/openapi-generator-cli.sh help
ls .bak/dowload
OPENAPI_GENERATOR_DOWNLOAD_CACHE_DIR="$(pwd)/.bak/download" bash bin/utils/openapi-generator-cli.sh help
ls .bak/download
bash bin/utils/openapi-generator-cli.sh help
ls bin/utils/openapi-generator-cli*

Then, test with another version:

export OPENAPI_GENERATOR_VERSION=4.1.0

And repeat the validations to verify.

[jimschubert]

@OpenAPITools/generator-core-team (since there's no technical committee for helper scripts)

[RonnyPfannschmidt]

yikes, what an oversight on my side, thanks for catching and applying a roundabout solution

[jimschubert]

No problem... It happens! Sorry I wasn't able to review the original PR. I've been playing catch-up for a few months.

[wing328]

This can be tested with:

OPENAPI_GENERATOR_DOWLOAD_CACHE_DIR="$(pwd)/.bak/dowload" bash bin/utils/openapi-generator-cli.sh help
ls .bak/dowload
OPENAPI_GENERATOR_DOWNLOAD_CACHE_DIR="$(pwd)/.bak/download" bash bin/utils/openapi-generator-cli.sh help
ls .bak/download
bash bin/utils/openapi-generator-cli.sh help
ls bin/utils/openapi-generator-cli*

@jimschubert what about adding it to the CI somehow? (assuming it's not a lot of work)

[jimschubert]

@wing328 This script just calls maven to get the .jar and (now) supports two environment variables. I don't think there's anything beneficial to test on every build for this. Manual testing on PR merges should suffice.

[wing328]

@jimschubert agreed. If it gains more activity/usage, we may consider adding a test to the CI later