[ofiwg] change proposal to provider API

[Hefty, Sean]

The following PR:

https://github.com/ofiwg/libfabric/pull/4874/files

makes a change to the fi_param_define() API.  This is an external API, which would be called by DL providers.  The change is to add a variable number of args in order to convert the help string into a help string format (~printf).

I tried some simple tests, and the change appears to be backward compatible.  Before merging, I wanted to publish the change to a broader audience for feedback.

- Sean