Update monitoring components

Update various monitoring components to latest upstream releases:
* Promehtheus 1.12.0 - Many changes, features, performance, bugfixes.
* postres_exporter 0.5.1 - Minor improvements.
* redis_exporter 1.1.0 - Minor imporvements.

No breaking changes introduced.

changelogs/unreleased/bjk-bump_prometheus_versions.yml

+---
+title: Update monitoring components
+merge_request: 3550
+author:
+type: other

config/software/alertmanager.rb

@@ -20,7 +20,7 @@ require "#{Omnibus::Config.project_root}/lib/gitlab/version"
 require "#{Omnibus::Config.project_root}/lib/gitlab/prometheus_helper"
 name 'alertmanager'
-version = Gitlab::Version.new('alertmanager', '0.16.2')
+version = Gitlab::Version.new('alertmanager', '0.18.0')
 default_version version.print
 license 'APACHE-2.0'

config/software/postgres-exporter.rb

@@ -19,7 +19,7 @@
 require "#{Omnibus::Config.project_root}/lib/gitlab/version"
 name 'postgres-exporter'
-version = Gitlab::Version.new('postgres-exporter', '0.4.7')
+version = Gitlab::Version.new('postgres-exporter', '0.5.1')
 default_version version.print
 license 'Apache-2.0'

config/software/prometheus.rb

@@ -20,7 +20,7 @@ require "#{Omnibus::Config.project_root}/lib/gitlab/version"
 require "#{Omnibus::Config.project_root}/lib/gitlab/prometheus_helper"
 name 'prometheus'
-version = Gitlab::Version.new('prometheus', '2.8.1')
+version = Gitlab::Version.new('prometheus', '2.12.0')
 default_version version.print
 license 'APACHE-2.0'

config/software/redis-exporter.rb

@@ -20,7 +20,7 @@ require "#{Omnibus::Config.project_root}/lib/gitlab/version"
 require 'time'
 name 'redis-exporter'
-version = Gitlab::Version.new('redis-exporter', '1.0.3')
+version = Gitlab::Version.new('redis-exporter', '1.1.0')
 default_version version.print
 license 'MIT'