build(webinstall): switch to distroless base image

[antoineco]

Prerequisite checklist

• Read the contribution guidelines regarding submitting new changes to the project;
• Tested your changes against relevant architectures and platforms;
• Ran make fmt on your commit series before opening this PR;
• Updated relevant documentation.

Description of changes

Use gcr.io/distroless/static:nonroot as the container base image for the following reasons:

• Already includes ca-certificates
• Rootless by default
• Enables the usage of secret injectors at runtime, which are often themselves injected as a static binary via Kubernetes mutating webhooks, and tend to fail if there is no basic directory structure inside the image (/tmp, ...)

[craciunoiuc]

All good here. Thanks!

Reviewed-by: Cezar Craciunoiu cezar.craciunoiu@unikraft.io
Approved-by: Cezar Craciunoiu cezar.craciunoiu@unikraft.io