Support storing & accessing secrets from within Kurtosis

[mieubrisse]

Background & motivation

This has been needed several times:

• For our internal dogfooding use of Kurtosis
• As a requirement for preview environments
• Various verbal requests from users
• https://discord.com/channels/783719264308953108/1131048810861314169/1215026889392001104

Desired behaviour

1. Kurtosis allows users to store secrets as strings within the Kurtosis engine
2. Secrets are stored securely, without risk of leaking (both locally, and more importantly in the Cloud)
3. Secrets are persistent through engine restarts
4. Users can reference secrets at any point by slotting in a future reference. At runtime, Kurtosis will replace the future reference with the actual secret value in a secure way (by communicating securely to the secrets manager)

@lostbean and I spec'd out a way to do Step 4 by injecting a wrapper binary into every secret-consuming user container that will securely pull the secret value at runtime. This has the extra benefit of the secret not even being revealed upon docker container inspect.

How important is this to you?

Painful; the lack of this feature makes using Kurtosis frictionful.

What area of the product does this pertain to?

CLI: the Command Line Interface