BUG #15880: ERROR: could not open extension control file "/usr/pgsql-11/share/extension/pgagent.control": No su

The following bug has been logged on the website:

Bug reference: 15880
Logged by: Shiwangini Shishulkar
Email address: shiwangini(dot)shishulkar(at)webgility(dot)com
PostgreSQL version: 11.3
Operating system: CentOS Linux release 7.6.1810 (Core)
Description:

To implement scheduling, we need use pgagent. For that, extension from
'https://ftp.postgresql.org/pub/pgadmin/pgagent/pgAgent-4.0.0-Source.tar.gz'.
And unzipped it to the location, from where it picks. Now, connected to sql
prompt as tried to create extension as per below:

[root(at)localhost pgAgent-4.0.0-Source]# su - postgres -c "psql"
psql (11.3)
Type "help" for help.

postgres=# \c postgres
You are now connected to database "postgres" as user "postgres".
postgres=# CREATE EXTENSION pgagent;
ERROR: extension "pgagent" has no installation script nor update path for
version "${MAJOR_VERSION}.${MINOR_VERSION}"

The last line error message i received which i'm not able to interpret.
Could you please help me with this. Any help will be appreciated. Also, if
there is any another way to configure/use pgagent then please share us the
link of doc.