add `AWS_PROFILE` support by allowing async configuration finalization

[CommanderStorm]

In the following PR AWS_PROFILE support was dropped, as it did not fit into the scope of the changes:

• feat(pmtiles)!: change pmtiles to base the implementation on object_storage instead #2251

Reintroducing AWS_PROFILE will require a smaller refactoring, changing the function signature from:

fn finish(&mut self) -> ConfigurationResult<()>

to

async fn finish(&mut self) -> ConfigurationResult<()>

This change will have follow-on effects throughout the codebase.

Tasks:

• Refactor finish to be async and propagate changes.
• add AWS_PROFILE support (and respective profile/aws_profile config variable) via the aws-config crate
• Validate integration and update relevant documentation.

[CommanderStorm]

CC people who are likely interested in this issue or know if this is even still necessary
@yharby @alamminsalo @jleedev

[jleedev]

Personally, I can't say I've used profiles, but they seem to be encouraged by the documentation, particularly when IAM/SSO are involved. Profiles are probably never used in the cloud -- a Lambda or container will have an environment with the access key and region in it; EC2 will use the metadata service, etc. Someone who is using profiles on their development machine can easily work around it in their config files, but might not immediately notice if this program reads the wrong config section.

On the object_store PR which removed the (broken) AWS_PROFILE support, someone suggested a warning when reading the environment variables and an AWS_* key is not understood, which I think would be a courteous thing for any program which is not 100% identical to the real AWS SDK.