Automatically append platform

> Note that Gradle resolves artifacts appropriate for a given platform

https://ktor.io/docs/server-dependencies.html#core-dependencies

... it turns out that bazel doesn't resolve the platform either -- which probably makes sense for it to be doing.

Makes it easier for folks to migrate or adapt instructions to bazel to not have to worry about `platform`.

Start by tracing how this repository resolves Maven artifacts and represents Gradle-style platform dependencies; the issue names no files, tests, or entry points. Confirm the expected Bazel dependency output for the Ktor instructions, then define completion as platform dependencies being appended automatically without requiring users to add platform themselves.

Written by the indexing model from the issue text.