Add missed salt api https proxy port to maas proxy conf

Change-Id: Ide7128cb553569715cf2020f6940cc4c586b7578
Related-Prod: PROD-33453
(cherry picked from commit 2546c09722452de9bfdcef770cc1fa0845d0fe90)
diff --git a/maas/files/maas-proxy.conf.template b/maas/files/maas-proxy.conf.template
index 99b0107..d085494 100644
--- a/maas/files/maas-proxy.conf.template
+++ b/maas/files/maas-proxy.conf.template
@@ -12,6 +12,7 @@
 acl localnet src {{cidr}}
 {{endfor}}
 acl SSL_ports port 443
+acl SSL_ports port 8969         # nginx salt api https proxy
 acl SSL_ports port 50000        # jenkins slave
 acl Safe_ports port 80          # http
 acl Safe_ports port 21          # ftp