Move template-field validation out of GoogleCampaignManagerDeleteRepo…

[bujjibabukatta]

Part of #70296.

Summary

Moves report_name / report_id validation in GoogleCampaignManagerDeleteReportOperator
from __init__ into execute(), and removes the class from the
validate-operators-init exemption list.

Root cause

report_name and report_id are template fields, which are rendered after the
constructor runs. Validating them in __init__ therefore checks the un-rendered
Jinja expressions instead of the actual values — the reason this class was on the
exemption list.

Fix

• campaign_manager.py — moved the "provide report_name or report_id" and
  "only one of them" checks from __init__ to the start of execute(); __init__
  now only does plain self.field = field assignments.
• validate_operators_init_exemptions.txt — removed the
  GoogleCampaignManagerDeleteReportOperator entry (required in the same PR; the
  hook fails on a stale exemption once the class is compliant).
• test_campaign_manager.py — added tests asserting both invalid cases (both
  provided / neither provided) now raise from execute().

Was generative AI tooling used ?

• Yes - Claude

Generated-by: Claude following the guidelines