[web][native] Support fetching Blob service URIs

Summary:
This diff adds support for fetching Blob service URIs for the native and web.

Depends on D7616

Test Plan:
Uploaded both encrypted and non-encrypted blob to local blob service instance.
Amended the keyserver's upload-fetchers to return these Blob URIs.
Verified media is fetched and displayed correctly both on web and native.

Reviewers: atul, marcin, ginsu, rohan

Reviewed By: atul

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D7617