Consider rename of OCDS API parameters version and index_version (or new param)

[kindly]

When the version parameter is used for the OCDS API endpoint it makes sense for the core standard.

https://github.com/OpenDataServices/standard-search/blob/master/standardsearch/webapp/views.py#L63

When used for profiles the version parameter should be

profiles/<profile_slug>/<branch>

and for infrastructure:

infrastructure/<branch>

Calling this parameter version could be considered confusing and its usage needs to not contain the start or end /