SOLR-17633 Add matomo script to doc index-page

[janhoy]

https://issues.apache.org/jira/browse/SOLR-17633

This adds matomo script to the index page of e.g. https://solr.apache.org/docs/9_8_0/ which is the landing page for each release. It does not attempt to add matomo script to the sub pages, such as changes or javadoc pages.

[janhoy]

Wdyt @epugh @dsmiley

I have manually patched https://solr.apache.org/docs/9_8_1/ with the tracker code. Once it is synced to the live site in a few hours, we should see that URL start popping up at the Matomo "pages" view, and then merge this PR to include for future releases.

[epugh]

Will check in a few hours. Thanks for doing this administrivia to keep our site up to date!

[janhoy]

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