Allow PI to upload data to Tier 0 and 1 environments

[martintoreilly]

:white_check_mark: Checklist

• [x] I have searched open and closed issues for duplicates.
• [x] This is a problem observed when using a Data Safe Haven.
• [x] I can reproduce this with the latest version.
• [x] I have read through the documentation.
• [x] This isn't an open-ended question (open a discussion if it is).

:computer: System information

• Data Safe Haven version: v0.3.0-beta
• Operating system details: All

:no_entry_sign: Describe the problem

Investigators do not have permission to bring data or code into tier 0 and 1 environments. Investigators should have one-step access to the ingress storage account in such cases.

:steam_locomotive: Workarounds or solutions

• Give investigators a SAS token for the ingress storage container in Tier 0 and 1 environments
• Update documentation and administrator processes to make this explicit.