Update myst-parser version for docs

[mosabua]

Description

Update myst-parser used in the docker container for builds to the new 1.0.0 release (from 0.18). This brings a bunch of improvements that are needed for the upgrade to markdown source for all the docs.

See https://myst-parser.readthedocs.io/en/latest/develop/_changelog.html

For this to be merged @electrum needs to build the container locally and push it to the ghcr with the updated 5.1 version. You can test this locally as well if desired with building the container and using SPHINX_IMAGE

Also note that GHA build will fail until the container is published. And we need to make sure we publish it as a dual processor architecture container as well so it performs well for x86 and arm/m1. Any tips how you did that last time @electrum ?

I ran full site build with old and new version and the output HTML is identical.

Additional context and related issues

This PR will help advance #17759 and follow up work.

Release notes

(x) This is not user-visible or docs only and no release notes are required.
( ) Release notes are required, please propose a release note for me.
( ) Release notes are required, with the following suggested text:

[mosabua]

@electrum published the container and we updated the version. All works now. Once approved I will merge.