Removed PGSM and pg_tde pages, added links to respective docs (#766)

Fixed links to pgsm install for apt and yum

modified:   docs/apt.md
	modified:   docs/extensions.md
	deleted:    docs/pg-stat-monitor.md
	deleted:    docs/pg-tde.md
	modified:   docs/telemetry.md
	modified:   docs/yum.md

Author: nastena1606

docs/apt.md

@@ -88,7 +88,7 @@ Run all the commands in the following sections as root or using the `sudo` comma
           $ sudo apt install percona-patroni
           ```
 
-          [Install `pg_stat_monitor`](pg-stat-monitor.md)
+          [Install `pg_stat_monitor` :octicons-external-link-16:](https://docs.percona.com/pg-stat-monitor/install.html):
 
 
           Install `pgBouncer`:

docs/extensions.md

@@ -4,12 +4,10 @@ Percona Distribution for PostgreSQL is not only the PostgreSQL server. It also i
 
 Percona Distribution for PostgreSQL includes the extensions that have been tested to work together. These extensions encompass the following:
 
-* [PostgreSQL contrib modules and utilities](contrib.md)
-* Extensions authored by Percona:
-  
-    * [`pg_stat_monitor`](pg-stat-monitor.md)
-    * [`pg_tde`](pg-tde.md) 
+Percona Distribution for PostgreSQL includes the extensions that have been tested to work together. These extensions encompass the following:
 
+* [PostgreSQL contrib modules and utilities](contrib.md)
+* [Extensions authored by Percona](percona-ext.md)
 * [Third-party components](third-party.md)
 
 Percona also supports [extra modules](https://repo.percona.com/ppg-16-extras/), not included in Percona Distribution for PostgreSQL but tested to work with it.