[Feature] openbb-platform-api Better POST Params Discovery

[deeleeramone]

This PR refactors the POST parameters discovery logic, which was originally intended for Forms. The logic now handles POST endpoints from the Provider Interface, and utilizes an alternative method for the Form endpoint and parameter discovery.

The changes to the README file describe the new situation, and the diff will show what changed.

Examples in the README have been updated accordingly.

Tests have been updated to reflect changes.

This should only be a breaking change if you have specifically implemented the Form logic somewhere.

For POST functions, the endpoint will not generate a widget if the widget_type is not one of widget types relying on the method:

• "ssrm_table"
• "omni"
• "multi_file_viewer"

None of the above widget types are assigned automatically, which effectively disables automatic widget creation for all POST endpoints, without basic user intervention - i.e, at minimum, {"openapi_extra":{"widget_config":{"type": "ssrm_table"}}