fix(algolia): don't fail to populate search container if one is "missing"

[msvticket]

Not all search containers might exist on a page. In that case an error like this is visible in the console:

Uncaught TypeError: can't access property "__k", t is null
    Ke https://cdn.jsdelivr.net/npm/@docsearch/js@3.8.2:8
    <anonymous> https://cdn.jsdelivr.net/npm/@docsearch/js@3.8.2:8
    <anonymous> https://jx-docs-jx-jayex-io-jx-docs-pr-19.infra.jenkins-x.rocks/:527

If it's #docsearch-0 that is missing, #docsearch-1 won't be populated even if it does exist.

My case

At https://jayex.io/ we are currently using custom code for Algolia but while I'm in the process of upgrading hugo and docsy I'm trying to switch to as much standard features as possible. The result for algolia was that the searchbox disappeared on the front page since it is configured to have no sidebars. Here is a link to my preview: https://jx-docs-jx-jayex-io-jx-docs-pr-19.infra.jenkins-x.rocks/

Maintenance

While fixing this I thought I'd do some maintenance as well:

• Upgrading docsearch to v4 since v3 isn't maintained.
• Switching to indices since indexName is deprecated: https://docsearch.algolia.com/docs/api#indexname
• Removing integrity as per https://www.jsdelivr.com/using-sri-with-dynamic-files