Parameterized deployment support

[colinjfw]

Allow deploying with variables that can be interpolated into the payload of the deployment. Similar to parameterized builds in Jenkins.

[jbergstroem]

Reading from a file in repo would be awfully convenient as well (that can be overwritten via the parameterized deploy).

Our use case are variables per environment that doesn't necessarily have to be classified as a github secret.

[missedone]

github slackbot support pass in the deployment payload: https://github.com/integrations/slack

however i'm looking for the same feature as well in deliverybot since i want to trigger the deployment either with slack or the web gui

thanks

[missedone]

ok, we can implement parameterize build with payload: https://deliverybot.dev/docs/configuration/#targetpayload

but noticed that the payload format is different with github slack.
deliverybot defines the payload as object (aka, JSON/Yaml object), while github slack is just raw string, it's inconsistent.
i'd suggest to support raw json string to be consistent with slack, Example:

prefer

production:
  environment: production
  production_environment: true
  payload: |
    {"foor": "bar"}

over

production:
  environment: production
  production_environment: true
  payload: 
    foo: bar