Add NetworkPolicy templates and passthrough values for alertmanager > mattermost connections

Add a NetworkPolicy template to each package conditional on the other application being enabled on BigBang to facilitate connection from alertmanager to mattermost to receive alerts.

• NP added to monitoring package conditional on mattermost.enabled
• NP added to mattermost package conditional on monitoring.enabled & possibly another variable
• Passthrough values added/verified in BB MR with above tag bumps

Package MR

big-bang/product/packages/monitoring!213 (merged)