[native] Add support for saving encrypted media

Summary:

• Passed through encryptionKey and blobURI down to the saveRemoteMediaToDisk() function
• In that function, added a separate flow for encrypted media. Basically, it has two steps:
  1. Download and decrypt media (decryptMedia()).
  2. Fetch MIME type

Depends on D10853

Test Plan:

• Tested on both Android and iOS
• Tested on both images and videos
• Also tested on prod keyserver inside Comm community, where prod app is crashing

Reviewers: atul, ashoat

Reviewed By: atul, ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D10854