feature: honour inputs for reusable workflows

Similarly explained at https://github.com/github/gh-aw/issues/29189

but the idea is

```yaml

on:
workflow_call:
inputs:
report-failure-as-issue:
default: true
description: When true, agent failures are reported as GitHub issues
required: false
type: boolean

...

GH_AW_FAILURE_REPORT_AS_ISSUE: ${{ inputs.report-failure-as-issue && 'true' || 'false' }}
```

this can help with configuring https://github.github.com/gh-aw/reference/safe-outputs/#failure-issue-reporting-report-failure-as-issue with some dynamism instead of using static code like

```
on:
workflow_call:

safe-outputs:
report-failure-as-issue: false

```

Why? Because otherwise, I need to use a post-compile hook:
- https://github.com/elastic/ai-github-actions/pull/1397/changes#diff-05c4ab4fb5cd2ca847da7ae17bd8477e5bba9e2300cb46d493e47ba49e5cd1b4

Start with the reusable-workflow and failure-issue-reporting behavior described in the issue and the linked safe-outputs reference. Compare the static configuration with the post-compile hook example; done means workflow_call inputs can dynamically control failure issue reporting without that hook.

Written by the indexing model from the issue text.