Obtain should take custom providers

The problem is that `$obtain` currently takes: `IPFSProvider` in provider parameter.

The task:
- extend that IPFSProvider is also `HTTP_URI`
- in mapper check if it's HTTP_URI than return that

Start at the implementation of `$obtain` and its provider mapper, checking how the current `IPFSProvider` parameter is handled. The work is complete when `HTTP_URI` is accepted as a provider and the mapper returns it correctly; inspect the relevant package tests or entry point to verify the behavior.

Written by the indexing model from the issue text.