[BUG] Using a path with a $ sign in it results in an error

Bug Report Checklist

• [x ] Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• [x ] What's the version of OpenAPI Generator used?
• [x ] Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

In an openapi file I want to specifiy a path with a $ symbol. eg:
/ActivityDefinition/{id}/$apply:
This is to define a FHIR-server like api.

openapi-generator version

4.3.1 and 5.0.0-snapshot using the docker images at: https://hub.docker.com/r/openapitools/openapi-generator-cli/

OpenAPI declaration file content or url

Use as a path:
/ActivityDefinition/{id}/$apply:

Generation Details

I used Docker image from https://hub.docker.com/r/openapitools/openapi-generator-cli/

docker run --rm -v ${PWD}:/local openapitools/openapi-generator-cli:v4.3.1 generate -i /local/myFile.yaml -g openapi-yaml -o /local/output

or (latest is currently 5.0.0-snapshot

docker run --rm -v ${PWD}:/local openapitools/openapi-generator-cli generate -i /local/myFile.yaml -g openapi-yaml -o /local/output

Steps to reproduce

Take an yaml file with a path like : /ActivityDefinition/{id}/$apply:

Related issues/PRs

Not found

Suggest a fix

This path is accepted in online editors like:
https://mermade.github.io/openapi-gui/
https://editor.swagger.io/

This should be accepted may be when quoting to complete path

Start with the reported /ActivityDefinition/{id}/$apply: path in myFile.yaml and run the provided openapitools/openapi-generator-cli Docker command using generator version 4.3.1 or the 5.0.0 snapshot. Confirm the failure and compare it with a path without the $ sign. Done means the path is accepted and generation completes successfully.