[BP to 7.2.5] - COUNT(*) on system:indexes can return incorrect results

This is a server ticket for https://couchbasecloud.atlassian.net/browse/AV-69973

Repro steps:

1. Load travel-sample dataset

2. Run the following queries:

a. 

select * from system:indexes

The result count of the above query:

"resultCount": 23

b.  Run a COUNT() against system:indexes without a predicate.

select count(*) from system:indexes;

The result is:

[

    {

        "$1": 33

    }

]

This is because the Count() implementation of the system:indexes keyspace does the following:

1. Counts the indexes created on the bucket i.e on the bucket’s default._default collection - _twice.

Since the Object is a keyspace and a bucket.

https://github.com/couchbase/query/blob/8de352393a1cb1a9c41d0bd1e6de9288dc9b663a/datastore/system/system_keyspace_indexes.go#L113

https://github.com/couchbase/query/blob/8de352393a1cb1a9c41d0bd1e6de9288dc9b663a/datastore/system/system_keyspace_indexes.go#L141