Update to use swift-openapi-generator 1.2.1

Changes:

• Uses v1.2.1 of swift-opernapi-generator
• Updates swift-package-manager to v0.30.0

For using this version, add this to the MODULE.bazel file instead:

bazel_dep(name = "swift-openapi-generator", version = "1.2.1")
archive_override(
    module_name = "swift-openapi-generator",
    integrity = "sha256-2vj0En8V30NhPrIxYN3oVoFxn/cX8jTHytuajdmCn5Q=",
    strip_prefix = "bazel-swift-openapi-generator-1.2.1",
    urls = ["https://github.com/Dreksh/bazel-swift-openapi-generator/archive/refs/tags/v1.2.1.tar.gz"],
)