fix: add idempotency_key, ignore_ssl_errors and do_not_retry to WebhookRepresentation

[vdusek]

Description

• Ad-hoc webhooks passed to start() / call() silently dropped idempotency_key, ignore_ssl_errors and do_not_retry because WebhookRepresentation declared only the four templating fields and encode_webhooks_to_base64 filters to declared fields. The platform accepts and honors all three for ad-hoc webhooks (verified in apify-core: the run-start handler feeds them into the same webhook-creation path as the create-webhook endpoint, including the idempotencyKey dedup).
• Adds the three fields to WebhookRepresentation, both webhook representation typed dicts, and the WebhookCreate projection in encode_webhooks_to_base64.
• The model and typed-dict edits match what regeneration will produce once fix(openapi): add missing ad-hoc webhook fields to WebhookRepresentation apify-docs#2640 (OpenAPI spec update) is merged and deployed.
• Unblocks fix: forward idempotency_key, ignore_ssl_errors and do_not_retry in ad-hoc webhooks apify-sdk-python#963, which forwards these fields from the SDK Webhook dataclass.

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.60%. Comparing base (9a953c7) to head (8afc3ad).

Files with missing lines	Patch %	Lines
src/apify_client/_typeddicts.py	0.00%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #854      +/-   ##
==========================================
- Coverage   94.82%   94.60%   -0.22%     
==========================================
  Files          48       48              
  Lines        5045     5063      +18     
==========================================
+ Hits         4784     4790       +6     
- Misses        261      273      +12     

Flag	Coverage Δ
integration	92.88% <33.33%> (-0.32%)	⬇️
unit	83.34% <33.33%> (-0.18%)	⬇️

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