Change documentation for CONTEXT environment variables

[npitsillos]

Describe your proposal/problem

The docs don't specify how to use context variables in a flow yaml.

It should be made clear that when defining a flow using the YAML specification VALUE_A & VALUE_B should appear in the env key.

---

Flow.yml

jtype: Flow
executors:
  - name: executor1
    uses: executor1/config.yml
    env:
      VALUE_A: 123
      VALUE_B: hello
    uses_with:
      var_a: ${{ CONTEXT.VALUE_A }}
      var_b: ${{ CONTEXT.VALUE_B }}

[npitsillos]

Looking at some of jcloud's integration tests the use of ${{ VAR_NAME }} or ${{ CONTEXT.VAR_NAME }} refers to the case of reading the value of the variable from a .env file. Whereas the use of ${{ ENV.VAR_NAME }} expects the var to appear in the env: clause of the yml syntax or as an environment variable.

That was the misleading part for me so maybe worth to reconcile between the two.

[jina-bot]

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