Manage config to run openapi generator in one file

[Yang-33]

Currently, the configuration for openapi-generator for line-bot-sdk-php is written in three workflows, which is a source of errors. Additionally, in the repository managing the OpenAPI schema, it's easy to forget to synchronize the settings.

One solution is to provide just one configuration file or script in this repository and have the CIs simply use it.

1. line-bot-sdk-php/.github/workflows/generate-code.yml

   Lines 31 to 51 in d012e5c

   	# Install openapi-generator-cli
   	- run: echo "OPENAPI_GENERATOR_VERSION=7.10.0" >> $GITHUB_ENV
   	- uses: actions/cache@v4
   	id: openapi-generator-cache
   	env:
   	cache-name: openapi-generator-cache
   	with:
   	path: ~/bin/openapitools
   	key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ env.OPENAPI_GENERATOR_VERSION }}
   	- if: steps.openapi-generator-cache.outputs.cache-hit != 'true'
   	run: |
   	mkdir -p ~/bin/openapitools
   	curl https://raw.githubusercontent.com/OpenAPITools/openapi-generator/master/bin/utils/openapi-generator-cli.sh > ~/bin/openapitools/openapi-generator-cli
   	chmod u+x ~/bin/openapitools/openapi-generator-cli
   	export PATH=$PATH:~/bin/openapitools/
   	OPENAPI_GENERATOR_VERSION=${{ env.OPENAPI_GENERATOR_VERSION }} openapi-generator-cli version
   	- name: Generate codes
   	run: |
   	export PATH=$PATH:~/bin/openapitools/
   	bash tools/gen-oas-client.sh

2. line-bot-sdk-php/.github/workflows/php-checks.yml

   Lines 34 to 54 in d012e5c

   	- name: Install openapi-generator-cli
   	run: echo "OPENAPI_GENERATOR_VERSION=7.10.0" >> $GITHUB_ENV
   	- uses: actions/cache@v4
   	id: openapi-generator-cache
   	env:
   	cache-name: openapi-generator-cache
   	with:
   	path: ~/bin/openapitools
   	key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ env.OPENAPI_GENERATOR_VERSION }}
   	- if: steps.openapi-generator-cache.outputs.cache-hit != 'true'
   	run: |
   	mkdir -p ~/bin/openapitools
   	curl https://raw.githubusercontent.com/OpenAPITools/openapi-generator/master/bin/utils/openapi-generator-cli.sh > ~/bin/openapitools/openapi-generator-cli
   	chmod u+x ~/bin/openapitools/openapi-generator-cli
   	export PATH=$PATH:~/bin/openapitools/
   	OPENAPI_GENERATOR_VERSION=${{ env.OPENAPI_GENERATOR_VERSION }} openapi-generator-cli version
   	- name: Generate code
   	run: |
   	export PATH=$PATH:~/bin/openapitools/
   	bash tools/gen-oas-client.sh

3. https://github.com/line/line-openapi/blob/0af4f53f23960ae0019526f631cf0fe81528e03f/.github/workflows/sdk-testing.yml#L133-L153

[Yang-33]

Other repositories use generate-code.py for this, so for consistency, it might be a good idea to do the same in this repository.