POC Complete key purpose markers

[dani-garcia]

Type of change

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

Objective

POC implementing working marker traits for encryption keys.

Some changes were needed to get this working:

• Split EncSettings::get_key into get_user_key and get_org_key, to have them typed correctly.
• Removed the org_uuid param from locate_key, as it didn't make sense anymore.
• Removed some impls from Encryptable which produced type conflicts with similar impls in KeyEncryptable.
• Implemented UserEncryption to OrgEncryption conversion to work around a mix up caused by EncryptionSettings using the single org key in secrets manager as the user key. This should be removed once we improve the EncryptionSettings situation.

TODO: Move functions like to_base64 and to_vec to a new Exportable purpose, to limit their use.