fix: add p7zip-plugins to base image for chectl

[SDawley]

Fix to previous PR. I noticed the image build failed because shasum is a perl script and not actually equivalent to sha1sum.

Issue: che-incubator/chectl#2239
The chectl package-binaries command also packages for windows and needs 7zip to do so.
I also noticed that the sizes in the readme were slightly out of date so I updated the compressed size to match the size in quay and the uncompressed size to how big they were when running locally.

Steps to reproduce:

• Create a Chectl workspace in the che dogfooding instance from https://github.com/SDawley/chectl/tree/contribute (my branch that contains the build fixes).
• Build Chectl
• Run the package-binaries command
  command fails:
  oclif-dev: building target chectl-win32-x64.tar.gz /bin/sh: 7z: command not found › Error: install 7-zip to package windows tarball error Command failed with exit code 2.

Steps to verify:

• Create a Chectl workspace in the che dogfooding instance from https://github.com/SDawley/chectl/tree/contribute. It uses the latest ubi image by default.
• Build Chectl
• Run the package-binaries command

[openshift-ci]

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This pull-request has been approved by: l0rd, SDawley

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