[ingest] Support multiple encryption keys

[nanjiangshu]

Main user story

As a security conscious user of the sensitive data arcive,
I want to see that the archive can rotate encryption keys
so that security can be maintained.

Sub user story

As an sda-dev
I want to implement multiple-key support for the ingest service
so that repository key rotation can be enabled.

Description

• Ingest should read a directory of private keys instead of just a single file
• Ingest should try all keys and add correct key hash to database

Acceptance criteria

• Demonstrate ingestion of encrypted files with two different archive c4gh private keys
• Tests verifying the changes are added

Extra information

Note: key rotation miro board here

Related issue for the verify service #1087.

[blankdots]

it would be good if this is left flexible/configurable as we do already have a mechanism to do that with https://github.com/CSCfi/c4gh-transit