After https://github.com/apache/spark/pull/30292, our Spark documentation site supports searching.
However, the default API key always points to the latest release doc. We have to set different API keys for different releases. Otherwise, the search results are always based on the latest documentation(https://spark.apache.org/docs/latest/) even when visiting the
documentation of previous releases.
As per discussion in https://github.com/apache/spark/pull/30292#issuecomment-725613417, we should make the API key configurable and avoid hardcoding in the HTML template.