Added pre-upgrade check for defect CSCwt69100

[Priyanka-Patil14]

Summary:
-This PR adds a new validation check: Stale dbgacEpgSummaryTask Objects.

-The check detects stale dbgacEpgSummaryTask objects stuck in processing state that can cause policymgr to crash on all APICs during upgrade (CSCwt69100).

What Changed:

• Added stale_epg_summary_task_check in aci-preupgrade-validation-script.py
• Added validation documentation in docs/docs/validations.md
• Added dedicated unit tests and test data under:
  tests/checks/stale_epg_summary_task_check/

Check Behavior:

• Returns `MANUAL' if target version is missing
• Returns N/A if target version is not in affected range (<= 6.1(5e) or <= 6.2(1g))
• Returns PASS if no dbgacEpgSummaryTask objects found in processing state
• Returns PASS if objects found but startTs is within 24 hours
• Returns FAIL_O if any dbgacEpgSummaryTask object has startTs older than 24 hours

Test Results:

• Pytest:
  CSCwt69100_Pytest_Logs.txt

• Full run (tversion 6.1(5e) and 6.2(2a)):
  CSCwt69100_FullRun_logs.txt