New server generator for Haskell/Yesod

[yotsuya]

Hello,
I've created a new generator named haskell-yesod.

• Type: Server
• Language: Haskell
• Web Framework: Yesod (https://www.yesodweb.com/)

PR checklist

• 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 (5.3.0), 6.0.x
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

[wing328]

@yotsuya thanks for the PR 👍

I did some tests locally and the result is good:

    returns 501 Not Implemented
  getUserLogoutR
    returns 501 Not Implemented
  putUserByTextR
    returns 501 Not Implemented

Finished in 0.0481 seconds
20 examples, 0 failures

open-api-petstore > Test suite open-api-petstore-test passed
Completed 17 action(s).

I'll merge it into master and file another PR for minor enhancements.