fix(editor): Handle large payloads in the AI Assistant requests better

[MiloradFilipovic]

Summary

1. Handling large payloads in AI assistant requests by trimming node parameters
2. Streaming the original error message from the server instead of always showing the generic Internal Server Error:
   

How to test:

Details are in this Linear comment.

Related Linear tickets, Github issues, and Community forum posts

Fixes ADO-3055

Review / Merge checklist

• PR title and summary are descriptive. (conventions)
• Docs updated or follow-up ticket created.
• Tests included.
• PR Labeled with release/backport (if the PR is an urgent fix that needs to be backported)

[codecov]

Codecov Report

Attention: Patch coverage is 97.55639% with 13 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
packages/editor-ui/src/api/ai.ts	41.66%	7 Missing ⚠️
...editor-ui/src/composables/useAIAssistantHelpers.ts	93.33%	3 Missing ⚠️
packages/editor-ui/src/stores/assistant.store.ts	94.11%	1 Missing ⚠️
packages/editor-ui/src/utils/apiUtils.ts	91.66%	1 Missing ⚠️
packages/editor-ui/src/utils/objectUtils.ts	95.23%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[mutdmour]

Can we please add more tests? This PR seems lacking in terms of coverage.

[MiloradFilipovic]

Can we please add more tests? This PR seems lacking in terms of coverage.

Alright, there are a few important bits that can be tested still.

[mutdmour]

Thank you for adding tests

[cypress]

n8n    Run #8887

Run Properties:   Passed #8887  •  e0d8e122f9: 🌳 🖥️ browsers:node18.12.0-chrome107 🤖 MiloradFilipovic 🗃️ e2e/*

Project	n8n
Branch Review	ADO-3055-ai-assistant-large-payload-handle
Run status	Passed #8887
Run duration	04m 38s
Commit	e0d8e122f9: 🌳 🖥️ browsers:node18.12.0-chrome107 🤖 MiloradFilipovic 🗃️ e2e/*
Committer	Milorad FIlipović
View all properties for this run ↗︎

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Test results
Failures	0
Flaky	1
Pending	0
Skipped	0
Passing	491
View all changes introduced in this branch ↗︎

[github-actions]

✅ All Cypress E2E specs passed