docs: Import searchtools.js

[dio]

Commit Message: This imports searchtools.js from https://raw.githubusercontent.com/sphinx-doc/sphinx/3.x/sphinx/themes/basic/static/searchtools.js.

Additional Description: #13005 (comment)
Risk Level: None
Testing: CI docs build
Docs Changes: N/A
Release Notes: N/A

Signed-off-by: Dhi Aurrahman dio@tetrate.io

[moderation]

@dio I was wondering if the searchgtools.js is available already as part of the pip3 install for Sphinx - https://github.com/envoyproxy/envoy/blob/master/docs/requirements.txt#L16. A little concerned that as this is a copy paste it could drift and be hard to maintain.

Edit: I just noticed #13005 (comment). Are we trying to override / update an existing version of this file beyond what is in Sphinx 3.2.1?

[dio]

@moderation yes, instead of building a full-theme. We override this to introduce small changes to it. I think when we bump (the major version of) Sphinx, that is the time we need to sync.