Allow using a single env template for multiple outputs

[Zeko369]

We're doing a multi-tenant SaaS where we deploy multiple environments per customer so we'd like to have a .env.[stage|production].erb that's used to generate all tenant envs i.e. .env.stage-microsoft or .env.production-google (instead of having 2 * number of tenants .env templates)

Something along the lines of bin/mrsk envify -d google -t .env.stage.erb -> .env.stage-google

Also to make this more configurable we'd use <%= ENV['MRSK_DESTINATION'] %> inside of the template to differentiate between destinations

[djmb]

We've removed kamal envify in Kamal 2