[REQ][Java] Set custom default parameter values in the client code

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

It would be nice to allow for (global) client-specific default values for query parameters in the generated API.
This would allow a client to use e.g. a custom paging default pageSize, deviating from the API provided default.
E.g. the API supports a default value of 100, but the client wants to fetch 1.000 by default.

Describe the solution you'd like

Allow to define custom default values for specified parameter names.
e.g. parameter limit: defaultValue: 1000
(API: default: 100)

Use those defaults in the generated client API code.

Describe alternatives you've considered

An alternative solution is to create local helper classes doing the initialization of the default values.
This works nice if only few methods need the custom default value.
However, if all paging methods should use a custom default value, this gets cumbersome.

Questions / Hints

• What would be the best place to add configuration for the custom default values?
• Modify the api.mustache file and check if {{paramName}} == null and then set the default value if available?
• Make sure this also works for API-specs using useSingleRequestParameter ("x-group-parameters": true)

Start with the Java client generation path and the api.mustache template mentioned in the issue. Compare how default parameter values are represented in generated methods, including APIs using useSingleRequestParameter ("x-group-parameters": true). Done means a client can configure global parameter defaults and generated paging methods use them without changing the API specification defaults.