cherry-pick: bamboo-specs: add missing vars

Merge in DNS/adguard-home from specs-vars to master

Squashed commit of the following:

commit 25f50e4
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Apr 30 15:12:28 2021 +0300

    bamboo-specs: add missing vars

bamboo-specs/release.yaml

@@ -4,6 +4,7 @@
   'project-key': 'AGH'
   'key': 'AGHBSNAPSPECS'
   'name': 'AdGuard Home - Build and publish release'
+# Make sure to sync any changes with the branch overrides below.
 'variables':
   'channel': 'edge'
   'dockerGo': 'adguard/golang-ubuntu:2.0'
@@ -261,6 +262,7 @@
     # need to build a few of these.
     'variables':
       'channel': 'beta'
+      'dockerGo': 'adguard/golang-ubuntu:2.0'
 # release-vX.Y.Z branches are the branches from which the actual final release
 # is built.
 - '^release-v[0-9]+\.[0-9]+\.[0-9]+':
@@ -270,3 +272,4 @@
     # are the ones that actually get released.
     'variables':
       'channel': 'release'
+      'dockerGo': 'adguard/golang-ubuntu:2.0'