Introduce ApiParameterMapper-Attribute Class

[DigitalTimK]

This PR will:

• push the array-generation inside of getHTTPQuery() into a separate toArray()-function
• introduce ApiParameterMapper-AttributeClass (new php8 feature), using at the getter of each parameter values to generate the former data array (see toArray()-function) automatically with toApiDataArray()-function.
• adapt getHttpQuery()-function to use new toApiDataArray()-function instead of toArray()-function
• set toArray()-function as deprecated (shall be removed once new concept is bullet prove)
• implement temporary test to ensure toArray()-function and toApiDataArray()-function deliver identical content

While working on the parameter generation this PR will improve in addition:

• MetaParameters-class
• UserDataParameters-class