Resolves #1131: Allow alternative Spark version

Resolve Docker lint (hadolint) errors

- Exclude `ppc64` Dockerfiles from the linting in pre-commit since we cannot check their build easily and so fix the lint errors without breaking something (already excluded in the `Makefile`)
- Fix examples Dockerfile to invert root and jovyan user instructions (Last user should not be root `DL3002`)

Allow to build `pyspark-notebook` image with an alternative Spark version.

- Define arguments for Spark installation
- Add a note in "Image Specifics" explaining how to build an image with an alternative Spark version
- Remove Toree documentation from "Image Specifics" since its support has been droped in #1115

Fix GITHUB_REPOSITORY value

Debug info for wiki push failure

Fix git-commit upstream

cd before configuring

[ci skip] Update stack READMEs

pre-commit hook + minor fixes

Pandas to 1.1

[ci skip] Fix wiki commit, 'ci skip' support

Fix git-commit var syntax

Combine jobs within workflows

Update doc, Dockerfile to test GH Actions

I originally tested in my fork where everything happened to be a push to a branch in the same repo.

Switch to GitHub Actions for CI/CD

Removed optional texlive-fonts-extra

Update scipy-notebook packages