Change simd base image to reduce image size

[chatton]

Summary of Bug

Currently we are using ubuntu:20.04 as the base image for simd/icad. We could switch to an alpine based image to reduce image size and result in a minor speed improvement in e2e. (more so for forks as we only build the image once when running e2e )

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For Admin Use

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[DimitrisJim]

side comment: we build simd for fork pr's using ubuntu-latest, we might want to keep them in-sync unless we switch e2e-fork.yml to re-use the workflow e2e.yaml uses.

Uses same Dockerfile, should be gtg.