[REQ] [PHP] support "original" mode for "variableNamingConvention"

[aghajani]

Is your feature request related to a problem? Please describe.

The modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractPhpCodegen.java file used by many php generators is supporting these values for "variableNamingConvention":

• camelCase
• PascalCase
• DEFAULT (any other value or empty) => snake_case

There are many scenarios which we want to use whatever defined in OpenAPI spec AS IS and without modification.

Describe the solution you'd like

I propose to add "original" to supported values and if set, we won't alter the names.