Modify the SQL++ used in the transaction documentation

The SQL++ statements used as examples for SQL transaction relies in primary index ie. where meta().id = '..' It was suggested that they are not as efficient as using USE KEYS.

https://docs.couchbase.com/server/current/n1ql/n1ql-language-reference/transactions.html#worked-example

In addition, there is no mention that these examples would not work for Capella. This is because of this https://couchbasecloud.atlassian.net/browse/AV-54183.

We should a note to say that the SQL++ transaction examples will not work in Capella Data Tools, but only with cbq shell.