feat: Password-protected AES-256 encrypted pastes

[jackdorland]

Please check the box if you understand that this repo is only for server-side backend issues. Please write issues related to the frontend or cli client in their respective repositories:

• [x] I understand.

Is your feature request related to a problem? Please describe.

N/A

Describe the solution you'd like

When pastes are uploaded, perhaps through a /encrypt endpoint, you would need to specify a password in the query parameters (or multipart form value). The server would then hash the password, salt it, encrypt the paste, and return the ID. No other data will be stored on the server other than the hash of the password.

Describe alternatives you've considered

N/A

Additional context

• First referred to in #24.

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