feat: Doc encryption with symmetric key

[islamaliev]

Relevant issue(s)

Resolves #2711

Description

This change introduces doc encryption. Upon creation of a document the user can pass an AES-GCM key for encryption.
This will lead to all doc fields (deltas) being stored in the DAG encrypted.
The storage in the local datastore happens as plain text (devs can enable encryption-at-rest to have it encrypted as well).

[fredcarle]

question: What do you think of naming it crypto instead? It's short enough and easier to figure out what it means.

[islamaliev]

it sounds better, but less relevant and 3 bytes longer.
I not happy myself with "enc" as it might not be immediatly clear, but tend to like it slightly more than "crypto". If other also see "crypto" being a better much (or anything else), no problem.

[fredcarle]

Overall I think you're going in the right direction. I have 2 main critiques at this stage. The first, as mentioned in an other comment, is the passing of a key on document create. I think we should avoid doing this and let Defra create a new key when needed. The second is the use of the context for the encryption key and store. It feels like it's making it more complex than it needs to be. We can discuss it some more in the standup or in a separate call if you want.

[codecov]

Codecov Report

Attention: Patch coverage is 80.10610% with 75 lines in your changes missing coverage. Please review.

Project coverage is 78.78%. Comparing base (8437805) to head (415b025).
Report is 8 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2731      +/-   ##
===========================================
- Coverage    78.85%   78.78%   -0.06%     
===========================================
  Files          315      318       +3     
  Lines        23835    24097     +262     
===========================================
+ Hits         18793    18984     +191     
- Misses        3670     3715      +45     
- Partials      1372     1398      +26     

Flag	Coverage Δ
all-tests	78.78% <80.11%> (-0.06%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
cli/collection_create.go	66.13% <100.00%> (+8.13%)	⬆️
client/document.go	71.92% <100.00%> (+0.12%)	⬆️
client/request/mutation.go	100.00% <ø> (ø)
datastore/multi.go	100.00% <100.00%> (ø)
http/client.go	56.33% <100.00%> (+0.54%)	⬆️
http/client_collection.go	43.46% <100.00%> (+1.63%)	⬆️
internal/core/block/block.go	90.65% <100.00%> (-0.57%)	⬇️
internal/db/collection.go	71.60% <100.00%> (ø)
internal/db/context.go	100.00% <100.00%> (ø)
internal/db/fetcher/fetcher.go	79.18% <100.00%> (ø)
... and 24 more

... and 13 files with indirect coverage changes

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