project.yaml can use URI scheme for job expressions and credential bodies

[taylordowns2000]

in a project.yaml, users should be able to specify URI paths to job expressions, rather than expressions as stings. See portability proposal v3: https://docs.openfn.org/documentation/portability#proposal-v3

Note how credentials are shaped: they either have keys and values inside a keyed object, or only have a path to the full body (i.e., some-credential.json)

jobs:
  job-1:
    expression: "alterState(state => ({ ...state, changed: true }))"
    trigger: trigger-1
  job-2:
    expression: file:///home/taylor/cool-job.js
    trigger: trigger-1
  job-3:
    expression: github:openfn/sample/myJob.js
    trigger: trigger-1
  job-4:
    expression: http://www.github.com/openfn/sample2.js
    trigger: trigger-1

credentials:
  my-secret-credential:
    username: '******'
    password: '******'
  my-other-credential: 'file://gcp_credential.json'

we should start with standard URIs, but maybe include some of the above.