Add a global option to customize the API name suffix

Created by: bgong-mdsol

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\. If contributing template-only or documentation-only changes which will change sample output, be sure to build the project first.
• Filed the PR against the correct branch: master, 4.1.x, 5.0.x. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

(details of the change, additional tests that have been done, reference to the issue for tracking, etc)

The problem: API generation for C#, Java and Ruby creates a class based on the tag and then adds "Api" after it. Ideally though we have a class like  "Study" or "Study{{Suffix}}" not "StudyApi".

I introduced a apiNameSuffix parameter in order to add suffixes to the generated api class/file/document names. Added the option "--api-name-suffix" to allow the user specify api name suffix via openapi-generator command line, the value of apiNameSuffix is "Api" if the option "--api-name-suffix" is not provided or empty.

Sample of command line: java -jar openapi-generator-cli.jar generate g java --api-name-suffix=client -i petstore.yaml -o out/petstore

This PR works for Java, Ruby, C# and Python

@jcarres-mdsol @bkashyapmd @jfeltesse-mdsol @prajon84 @ykitamura-mdsol @cabbott