Improve the secrets file docs

[spkane]

Adding some more thorough examples since the documentation is sparse here and in the upstream library. I basically had to write a test application and read some various docs about the .env format to figure the logic out.

[spkane]

@ashwilliams1 Is there someone specific who can review this? I don't believe it needs any updating unless someone wants to simply ensure that it is correct.

[bradrydzewski]

we would probably want to document the env file format in a separate, dedicated page, and then link to that page from the quick start. The env file is used in multiple places (not just the drone exec) so having a separate reference document would be preferred. This also keeps are quick starts high level.

[spkane]

That makes sense. I'll leave you all to it then. I just hope that something gets merged in soon-ish, as this took some time to track down and needing to pass in something like an SSH key is a standard enough use case that this should help others avoid the difficulty of figuring this out themselves or just giving up.

[shyandsy]

for docker-build, the secret DOCKER_USERNAME and DOCKER_PASSWORD works well, docker image push successfully

but why I cant retrive these secret in test-secrets?

it should work, right?
base on the doc :https://docs.drone.io/secret/repository/

- name: test-secrets
  image: alpine:3.19
  environment:
    DOCKER_USERNAME:
      from_secret: DOCKER_USERNAME
    DOCKER_PASSWORD:
      from_secret: DOCKER_PASSWORD
  commands:
    - echo $USERNAME
    - echo "USERNAME => ${DOCKER_USERNAME}"
    - echo "PASSWORD length => ${#DOCKER_PASSWORD}"
    
- name: docker-build
  image: plugins/docker
  settings:
    dockerfile: Dockerfile
    repo: shyandsy/whoispua
    tags:
      - api_${DRONE_BRANCH//\//-}_${DRONE_COMMIT_SHA:0:7}
    username:
      from_secret: DOCKER_USERNAME
    password:
      from_secret: DOCKER_PASSWORD
    #push: false
  when:
    event:
      - push
      - tag