[Gradle Plugin] Fix registering Gradle tasks when apply plugin to project (!10079) · Merge requests · OpenAPI Tools / openapi-generator

Created by: kuFEAR

Fixed registration of Gradle tasks when applying the plugin to the project using the task avoidance API. https://docs.gradle.org/current/userguide/task_configuration_avoidance.html

It creates 4 tasks for each gradle module where openapi generator plugin is applied, but with change create->register it will created on demand.

Read the contribution guidelines.
Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
Run the following to build the project and update samples:
```
./mvnw clean package 
./bin/generate-samples.sh
./bin/utils/export_docs_generators.sh
```
Commit all changed files. This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master. These must match the expectations made by your contribution. You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*. For Windows users, please run the script in Git BASH.
File the PR against the correct branch: master, 5.3.x, 6.0.x
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