examples: Flesh out Makefile-based example

[simonjbeaumont]

Motivation

We have an example project showing ahead-of-time generation using the swift-openapi-generator CLI directly, driven by a Makefile. This PR polishes it up a bit and makes it more flexible. Additionally, the generated code had not been updated since we switched the default access modifier from package to internal.

Modifications

• Allow overriding a bunch of things when calling make.
• Prompt for confirmation before blowing away the output directory.
• Regenerate sources to pick up the new access modifier.
• Add a help target.

Result

More extensive example.

E.g. running the following command:

% make help
Run make with one of the following targets:

  help:          Display this help.
  generate:      Generate the sources using swift-openapi-generator.
  build:         Runs swift build.
  clean:         Delete the output directory used for generated sources.
  clean-all:     Clean everything, including the checkout of swift-openapi-generator.
  dump:          Dump all derived values used by the Makefile.

The following options can be overriden on the command line:

  SWIFT_OPENAPI_GENERATOR_GIT_URL (e.g. https://github.com/apple/swift-openapi-generator)
  SWIFT_OPENAPI_GENERATOR_GIT_TAG (e.g. 1.0.0)
  SWIFT_OPENAPI_GENERATOR_CLONE_DIR (e.g. .swift-openapi-generator)
  SWIFT_OPENAPI_GENERATOR_BUILD_CONFIGURATION (e.g. release)
  OPENAPI_YAML_PATH (e.g. openapi.yaml)
  OPENAPI_GENERATOR_CONFIG_PATH (e.g. openapi-generator-config.yaml)
  OUTPUT_DIRECTORY (e.g. Sources/ManualGeneratorInvocationClient/Generated)

Test Plan

CI should still build the package.

[czechboy0]

Just one suggestion