SearchQuery should be SearchQueryAsync in docs

@cbfts
In the documentation on [Searching with the SDK](https://docs.couchbase.com/dotnet-sdk/current/howtos/full-text-searching-with-sdk.html#examples) it says `var result = cluster.SearchQuery(`. This brings up a compile error and when I search for "SearchQuery" in the api docs I can't find anything. I looked at the docs page for cluster and can see the method "SearchQueryAsync" so I've changed it to that. Do you see this causing any issues compared to the version in the docs?