[Typescript] Improve exception for unknown responses

Created by: bodograumann

For http errors that are not explicitly defined in the api specification, currently the consolidated typescript generator does not retain the body. Instead a generic [object Object] string is provided for it in the error message. This is probably an oversight.

Instead we now set the message string and response body attributes on the exception object separately. Additionally I have added a heuristic which tries to parse the response as JSON, falls back first to plain text, then to binary and then to undefined.

I have added a new deleteNonExistantPet integration test to the default typescript/node petstore sample.

This is a template-only change.

Steps:

• Clean up tests
• Change tests to async-await
• Use different pets for each test
• Add test for unknown error response code
• Make body of unexpected error responses available
• Regenerate all consolidated typescript samples

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.

CC @TiFu (2017/07) @taxpon (2017/07) @sebastianhaas (2017/07) @kenisteward (2017/07) @Vrolijkx (2017/09) @macjohnny (2018/01) @topce (2018/10) @akehir (2019/07) @petejohansonxo (2019/11) @amakhrov (2020/02)