docs: document external HTTP GET schema example

[zmstone]

No description provided.

[Copilot]

Pull request overview

Updates the External HTTP schema registry documentation to cover calling external schema endpoints via HTTP GET in addition to POST, including request/query parameter details and corresponding example/server updates.

Changes:

• Document GET request format (query parameters, URL-safe Base64 without padding, and query-string appending behavior).
• Add a “Schema Configuration Reference” section describing Dashboard fields (including the new Method selection guidance).
• Update the Flask example to accept both POST and GET, and decode URL-safe Base64 for GET.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
zh_CN/data-integration/schema-registry-example-external-http.md	Adds GET request spec, configuration reference table, and updates the Python example + Dashboard instructions (contains a small typo).
en_US/data-integration/schema-registry-example-external-http.md	Adds GET request spec, configuration reference table, and updates the Python example + adds Method guidance.

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