[REQ] Remove `mvn` as dependency for `openapi-generator-cli.sh`.

Is your feature request related to a problem? Please describe.

Describe the solution you'd like

You could directly curl the jar file like so:

curl -O "${repo}/org/openapitools/openapi-generator-cli/${tagname}/openapi-generator-cli-${tagname}.jar"

Both repo and tagname are already known so, nothing else would need to be changed.

Describe alternatives you've considered

Most users could do this change by themself is they actually did care (like I did), but I think it would be better to just remove a dependency that most people would not have on their machines.

Open Questions

• Does this change opens vulnerabilities that weren't possible using mvn maven-dependency-plugin:2.9?

Start by locating openapi-generator-cli.sh and read how it currently invokes mvn maven-dependency-plugin:2.9, including how repo and tagname are set. Check the script's existing download and execution flow, then verify that replacing the Maven-based retrieval with the proposed curl command still obtains the expected CLI JAR without changing other behavior.