Add required tools to the codespace image

[anayden]

This adds chafa and just to the dev image.

One can play with it via

P.S. Don't forget to shutdown your codespace when you don't need it
P.P.S. Note this also adds chafa to the base image for future usage in R2DT

[github-actions]

Docker image tag(s) pushed:

rnacentral/r2dt:pr-127

Labels added to images:

org.opencontainers.image.created=2023-12-07T22:16:18.011Z
org.opencontainers.image.description=Visualise RNA secondary structure in consistent, reproducible and recognisable layouts
org.opencontainers.image.licenses=Apache-2.0
org.opencontainers.image.revision=f20ec09e9a1a286c1d14882f422e637c50021ecc
org.opencontainers.image.source=https://github.com/RNAcentral/R2DT
org.opencontainers.image.title=R2DT
org.opencontainers.image.url=https://github.com/RNAcentral/R2DT
org.opencontainers.image.version=pr-127

[AntonPetrov]

@anayden I am very sorry for taking so long to review this PR but I tested it and it worked! 🎉👏

During my testing, I created a Codespace based on this branch, ran just run to get an image, then did r2dt.py test TestTemplateFree to get a thumbnail image, then exited the container, and ran chafa to view the thumbnail in console.

In general, this PR lays the groundwork for 2 cool features:

1. using R2DT in Codespaces (which seems to work well and can be merged now so that one can do further testing and try to use it for actual development). What do you think about adding an Open in Codespaces badge in Readme?
2. viewing SVGs in console by adding a new flag to r2dt.py. For example, by default it does not show the 2Ds but with --view-results or similar it would show all images from the thumbnail folder.

I am ready to merge this PR, if you think it's ready. Alternatively, we can add more functionality in this branch - up to you!

Thank you again for bravely exploring the new territory and adding exciting new capabilities to R2DT!

[anayden]

Hey, thanks for looking into it. I've added the badge to README.md and I think it's time to merge (if you're okay with the badge placement)