[aws-region] Custom endpoint require to end without slash

**Describe the bug** I don't know if it's a "bug" or a feature request. I just found that the slash at the end of the endpoint for custom region leads to 403, Signature Miss Match It's weird because the provider provide the endpoint with the slash and `aws-cli` support the ending slash. Also found in the example there was no slash, which resolve my issue. **To Reproduce** Create a custom Region with endpoint ending with slash Error with: `https://s3.gra.io.cloud.ovh.net/` Working with: `https://s3.gra.io.cloud.ovh.net` **Expected behavior** Not a 403 **Environment** - Rust version: [`1.85.0`] - lib version [`0.35.1`]