Update GSE search in index.html

https://raw.githubusercontent.com/infinispan/infinispan/main/documentation/src/main/asciidoc/index.asciidoc

++++
<script async src="https://cse.google.com/cse.js?cx=013815398149802919631:_cym2xwxalo"></script>
<div class="gcse-search"></div>
++++

Modify/update the script to return more accurate search results. Maybe it's the case that the script needs to be regenerated or refreshed to pick up recent changes in documentation, like the addition of the marshalling/encoding guide.

iirc that google search script is tied to your account NadirX