Update references of `orchestrationClient` to `durableClient`

Previously, the durable client input binding type was called `orchestrationClient`. That name, while still supported, was deprecated in favor of `durableClient` (since durable clients can be used to interact with more than just orchestrations). We should update our templates, samples, and docs to reflect that change and not use `orchestrationClient`.

Search the repository's templates, samples, and documentation for references to `orchestrationClient`, then review each occurrence in context. Update the relevant references to `durableClient` while preserving the documented compatibility note, and confirm that no targeted template, sample, or documentation reference still uses the deprecated name.

Written by the indexing model from the issue text.