Link to the Jira issue: https://issues.apache.org/jira/browse/ARROW-18363.

This PR inserts a script element into all .html files which calls a /docs/versionwarning.js file. The file adds a version warning to the .html page if the file path matches any of the 4 criteria:

• the page is under developers section in stable release
• the page is in the docs for arrow version older then 4.0
• the page is under developers section and in the docs for older arrow version (but at least 4.0)
• the page is in the docs for older arrow version (but at least 4.0)

Each of these warnings has its own warning message.

This PR is a part of Jira to GitHub migration work.

Hot to test the code locally?

1. Checkout any commit from arrow-site/asf-site other than this one
2. Save versionwarning.js to arrow-site/docs/ folder
3. Run next code snippet in the terminal (for MacOS, should be a bit different for Linux/Wind) from the arrow-site/docs folder. You will have to check/correct numbers 6&7 from the snippet.
   My path to arrow-site/docs is /Users/alenkafrim/repos/arrow-site/docs and is a "length" of 5 so numbers I used down below were 6&7. If the length of you path is 7 then you need to change 6 with 8 and 7 with 9 😬
   I am searching for a shell function to give the length and I can automate this step =)

# Run this from the arrow-site/docs/ folder (check the numbers 6&7!)
sed -i '' "s/'arrow.apache.org')/'')/" versionwarning.js
sed -i '' "s/\[2\]/\[6\]/" versionwarning.js
sed -i '' "s/\[3\]/\[7\]/" versionwarning.js
sed -i '' "s/(2)/\(6\)/" versionwarning.js
sed -i '' "s/(3)/\(7\)/" versionwarning.js

# insert the JS file into all the html files in /docs
find . -iname "*.html" | xargs sed -i '' '/<\/body>/ i\
<script type="text/javascript" src="/docs/versionwarning.js"></script>'

This is the visual from my local tests: