Set custom endpoint uri

I want to use custom endpoint URL to use s3pathlib with Minio.

From the documentation below, I can see it is easy to change many parameters, but not the endpoint_url which is defined inside the client. And in resolve_s3_client, context.s3_client returns a new client so it is not possible to change its endpoint.

```
from s3pathlib import context
context.attach_boto_session(
boto3.session.Session(
region_name="us-east-1",
profile_name="my_aws_profile",
)
)
```

I would like to change the endpoint so I can use a self hosted minio instead of default AWS endpoint.