infra: update copy druid script

[317brian]

Docusaurus 3 uses MDXv3, which is much stricter.

The longstanding way we've done variables is to find/replace {{DRUIDVERSION}} in the Markdown files. It worked in 2 b/c 2 was less strict. 3 is stricter and picks them up as Javascript variables that are undefined.

Instead of making people learn a new way to do variables, this updates the copy script so that an escaped version of \{\{DRUIDVERSION}} (and variations) also get find/replaced

We would have to do a find/replace anyway unless we set up the variables to match each other in druid-website-src and druid

To verify this, check out the Markdown cleanup branch in apache/druid#17740 and run the copy script in scripts.

Then grep for DRUIDVERSION in the markdown files and maybe whatever version you set, eg 32.0.0

grep -ir 'DRUIDVERSION' ./docs

grep -ir '32.0.0' ./docs

[vtlim]

LGTM 🦖

Tested using these commands. Spot checked several pages with DRUIDVERSION variable and they resolved correctly.

# build
python do_all_things.py -v 32.0.0 --skip-install --source ../../druid-apache

# preview
npm run serve

There's a syntax warning but it raises on the docstring so doesn't affect anything

/Users/victorialim/Documents/work_repos/druid-website-src/scripts/copy_druid_docs.py:61: SyntaxWarning: invalid escape sequence '\{'