Add possibility to limit deploying on deploy stage

Travis CI Discussions & Feedback
1

When there are multiple stages (including a specifi deploy stage) and multiple jobs in the deploy stage then it would be nice to have global deploy settings but limit them to the deploy stage (without using an environment variable).

Example:

stages:
  - test
  - deploy

jobs:
  include:
    - env: TYPE=1
      script: some_commad
    - env: TYPE=2
      script: some_commad
    - stage: deploy
      env: TYPE=1
      script: some_commad
    - stage: deploy
      env: TYPE=2
      script: some_commad

deploy:
  provider: xxx
  api_key: xxx
  on:
    stage: deploy  # This currently do nothing
2

Put the deploy definition in the relevant jobs. If you do not want definition repeated, use YAML anchors.