Pass environment variable $fre_yaml to plugin scripts that points to yaml

[ceblanton]

Describe your changes

Issue ticket number and link (if applicable)

#223

Checklist before requesting a review

• I ran my code
• I tried to make my code readable
• I tried to comment my code
• I wrote a new test, if applicable
• I wrote new instructions/documentation, if applicable
• I ran pytest and inspected it's output
• I ran pylint and attempted to implement some of it's feedback
• No print statements; all user-facing info uses logging module

Manual Pipeline Run Details

Was the manual pipeline (test_cloud_runner) triggered for this PR?

• Yes
• No

Result of manual pipeline run:

(Paste relevant logs, output, or a link to the workflow run here)

How to trigger the manual pipeline:

The test_cloud_runner pipeline is not automatically associated as a required check with the PR; it must be triggered to test changes in a full post-processing run.

To trigger the manual pipeline:

1. Follow the link to the test_cloud_runner actions tab here

   • you should see "This workflow has a workflow_dispatch event trigger"

2. Click the dropdown "Run workflow":

   a. If trying to merge from a branch on fre-workflows: choose branch from the first drop down, leave the next 2 inputs blank, and choose the fre-cli branch to test

   b. If trying to merge from a fre-workflows fork: can skip first branch selection, input the fork name (ex: [user]/fre-workflows), input the fork's branch name, and choose the fre-cli branch to test

3. Click "Run workflow"

Note: you may need to reload the page to see your running workflow.

[Copilot]

Pull request overview

This PR makes the combined experiment YAML path available to all Cylc tasks (and therefore plugin scripts) via a single inherited environment variable, addressing the need for preanalysis scripts to locate and parse the YAML configuration.

Changes:

• Define fre_yaml once at [runtime][[root]][[[environment]]] as $CYLC_WORKFLOW_RUN_DIR/{{ YAML }}.
• Remove per-task yaml_config environment definitions and switch callers to use $fre_yaml.

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