doc: Document paramgen for conduit developers

[hariso]

Feature description

As the title implies.

I'm thinking of implementing the custom ordinal table key for table using Dynamic configuration parameters
can't find the docs for it in conduit, although I don't really know where should it be documented (developing conduit > connectors / pipelines > configuration file?). The article is the only thing I found.

Workaround

right now, unfortunately the best we can do is to provide examples from other connectors. One is the generator https://github.com/ConduitIO/conduit-connector-generator/blob/main/config.go#L50
example config: https://github.com/ConduitIO/conduit-connector-generator?tab=readme-ov-file#collections