Add pre-commit hooks

[bbannier]

This adds a number of formatters and linters.

[timwoj]

Some of the line breaks added by prettier in the jinja templates might break things. Jinja can be a bit finnicky sometimes, in my prior experience.

[bbannier]

Some of the line breaks added by prettier in the jinja templates might break things. Jinja can be a bit finnicky sometimes, in my prior experience.

I had tried to format the template HTML files with prettier and tried to manually back out problematic files, but I might have screwed up. I reverted this and now do not format any template files anymore (identified by their path which is excluded by pre-commit).