Agent Engine: add source based deployment documentation.

[LucaPrete]

google_vertex_ai_reasoning_engine

• Adds source based deployment documentation
• Fixes min/max instances documentation

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vertexai: added example for source based deployment in `vertex_ai_reasoning_engine` resource documentation

[github-actions]

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[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

google provider: Diff ( 1 file changed, 30 insertions(+))
google-beta provider: Diff ( 1 file changed, 30 insertions(+))

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

google provider: Diff ( 2 files changed, 41 insertions(+), 11 deletions(-))
google-beta provider: Diff ( 2 files changed, 41 insertions(+), 11 deletions(-))

[modular-magician]

Tests analytics

Total tests: 83
Passed tests: 80
Skipped tests: 3
Affected tests: 0

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• vertexai

🟢 All tests passed!

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[github-actions]

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