support signed pipelines

[raylu]

Is your feature request related to a problem? Please describe.
no

Describe the solution you'd like
https://buildkite.com/docs/agent/v3/signed-pipelines#enabling-signed-pipelines-on-your-agents-step-2-configure-the-agents
requires configuring the agents. if we use this stack, there isn't an easy way to do that

Describe alternatives you've considered
writing the config in a bootstrap hook

Additional context

[wolfeidau]

@raylu I will raise this internally and get back to you with some suggestions.