citool: set TMT_IMPORT_BEFORE_FILTER=1 by default

Summary

Set TMT_IMPORT_BEFORE_FILTER=1 in worker environment-variables and add TMT_IMPORT_BEFORE_FILTER to accepted-environment-variables across all 18 test-schedule-tmt* configs (dev, staging, production).

Why: tmt 1.62 (teemtee/tmt#4261) added TMT_IMPORT_BEFORE_FILTER to fix teemtee/tmt#4231 — imported plans could not be discovered by --name, breaking Testing Farm for any repo using plan.import. The follow-up on the TF side never happened, so the bug is still live.

What this does:

• Appends TMT_IMPORT_BEFORE_FILTER=1 to environment-variables — enables import-before-filter by default for all TF runs
• Adds TMT_IMPORT_BEFORE_FILTER to accepted-environment-variables — lets users override it (e.g. =0) for edge cases like teemtee/tmt#4757 (inaccessible plan.import URLs)

This follows the existing pattern used by TMT_REPORT_ARTIFACTS_URL (set as default + listed as accepted).

Once teemtee/tmt#4923 lands and import-before-filter becomes the tmt default, the environment-variables entry can be removed.

Resolves: TFT-4753

Assisted-by: Claude Code