replication slots only need user with replication for creation

Hi,

Looking at privileges that a user would need now a days to create a
cluster clone with repmgr we noticed that there's inaccurate information
in the docs regarding the use of replication functions.

I was able to test on 9.6 and 10 that a user with replication privileges
can create and drop a replication slot.

But in the system administration functions, section replication
functions it states:

The functions shown in Table 9.83 are for controlling and interacting
with replication features. See Section 26.2.5, Section 26.2.6, and
Chapter 49 for information about the underlying features. Use of these
functions is restricted to superusers.

Source:
https://www.postgresql.org/docs/10/static/functions-admin.html#FUNCTIONS-REPLICATION

I suggest amending this with a text like the following:

The functions shown in Table 9.83 are for controlling and interacting
with replication features. See Section 26.2.5, Section 26.2.6, and
Chapter 49 for information about the underlying features. Use of these
functions is restricted to superusers and users with replication privileges.

I think this doc patch should be back-patched

Regards,

-- 
Martín Marqués                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services