State explicitly that sizeOnDisk already includes indexSize

Description

In https://docs.mongodb.com/manual/reference/command/listDatabases/index.html, it states:

A sizeOnDisk field with the total size of the database files on disk in bytes.

and

The sizeOnDisk field represents the total size of all listed collections.

So we already state that it represents the actual total size on disk, therefore it is including the byte count of the indexes.

In order to be very clear, I suggest we change the second quote to:

The sizeOnDisk field represents the total size of all listed collections (including indexes).

Scope of changes

Impact to Other Docs

MVP (Work and Date)

Resources (Scope or Design Docs, Invision, etc.)