Fix #210: [Ada] Update the code generator for required and optional parameters

Created by: stcarrez

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 and ./bin/security/{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\.
• Filed the PR against the correct branch: Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

Fix for #210 (closed)

• Do not check for required parameter in getTypeDeclaration()
• Update the nullableTypeMapping map to map an Ada type into a corresponding Nullable_ Ada type that allows the value to be null
• Check for optional parameter in postProccessOperations() and postProcessModels() to replace the Ada type into an Ada type that supports null values