Document SELECT projection order changes

Probably to be added to:

https://docs.couchbase.com/server/current/n1ql/n1ql-language-reference/selectintro.html

Before MB-53938 the terms listed in the projection were returned in alphabetical order.  With this change, they are now returned in the order specified.  (The contents of composite items are unaffected.)  So perhaps:

(after) "With projections, you retrieve just the fields that you need and not the entire document. This is especially useful when querying for a large dataset as it results in shorter processing times and better performance."

(add) "The projection is returned in the order specified.  In prior versions it was sorted alphabetically.  To revert to this behaviour, use the sort_projection request parameter."

https://docs.couchbase.com/server/current/settings/query-settings.html#section_nnj_sjk_k1b

Needs to have an entry added:

sort_projection

Causes statement projection terms to be sorted alphabetically.