Use ubuntu 20 as the docker base image

[Kailai-Wang]

Context

We are currently using ubuntu 22.04 as the base image for packaging the parachain binary.

It works fine in CI but we have problems when:

• we launch the parachain on dev server
• we deploy the production

The builder env needs to double-checked too (rust:latest)

As in both cases we copy the binary from the docker image and run it locally. We'll get GLIBC error when running on a ubuntu20 host (via make launch-docker-rococo):

stderr: "generated-rococo/litentry-collator: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.33' not found (required by generated-rococo/litentry-collator)

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