[Feature request] Shareable grpcui link that auto-populates request

`grpcui` doesn’t put the method and the request body in the URL's query parameter which makes it difficult to share the repro of an issue with another engineer. Can we provide a way to create a `grpcui` shareable link that will auto-select the service, method, and request when someone opens that link?

Start by inspecting how grpcui currently represents the selected service, method, and request in its URL and how the web UI reads query parameters. Define the shareable-link format and verify that opening it auto-selects the service and method and restores the request body; the issue names no files or tests to run.

Written by the indexing model from the issue text.