[Bug]: Backup configuration doesn't trim trailing white space

### Problem description

When trying to set up Deno KV backups to Google Cloud Storage, Google's interface for generating access tokens includes a single trailing space at the end of the access key:

When pasting this into Deno, it can be easy to miss this trailing white space, resulting in the backup failing.

### Steps to reproduce

1. Set up a backup configuration for Deno KV
2. Add a trailing whitepsace to the access key
3. Observe the backup fails

### Expected behavior

Forms that accept copy/pasted tokens should trim leading and trailing white space.

### Environment

_No response_

### Possible solution

_No response_

### Additional context

_No response_

Begin at the Deno KV backup configuration form and reproduce the issue by entering an access key with trailing whitespace. Trace how the credential is accepted and used, then verify that a backup succeeds when the key is pasted with leading or trailing whitespace.

Written by the indexing model from the issue text.