[PM-5348] Encrypt/decrypt attachment files

[dani-garcia]

Type of change

- [ ] Bug fix
- [x] New feature development
- [ ] Tech debt (refactoring, code cleanup, dependency upgrades, etc)
- [ ] Build/deploy pipeline (DevOps)
- [ ] Other

Objective

Add encryption/decryption support for attachment files

[codecov]

Codecov Report

Attention: 159 lines in your changes are missing coverage. Please review.

Comparison is base (c1badb7) 50.47% compared to head (7d61bc6) 50.01%.
Report is 3 commits behind head on main.

Files	Patch %	Lines
crates/bitwarden-uniffi/src/vault/attachments.rs	0.00%	78 Missing ⚠️
...s/bitwarden/src/mobile/vault/client_attachments.rs	0.00%	60 Missing ⚠️
crates/bitwarden/src/vault/cipher/attachment.rs	78.31%	18 Missing ⚠️
crates/bitwarden-uniffi/src/vault/mod.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #490      +/-   ##
==========================================
- Coverage   50.47%   50.01%   -0.47%     
==========================================
  Files         157      159       +2     
  Lines        7564     7788     +224     
==========================================
+ Hits         3818     3895      +77     
- Misses       3746     3893     +147     

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[Hinton]

I think we can better encapsulate the attachment key.

[Hinton]

I think we're missing the use case of creating an attachment. Which also involves creating the key.

I think what we want is a way to create a new attachment which also creates a key. And a way to decrypt existing attachments. There should be no need to use an existing key to encrypt again.