website: S3 module sources now support all standard AWS credential sources

As of go-getter v1.8.0, which we already upgraded in an earlier commit,
the S3 "getter" now uses the AWS SDK's default credentials chain
configuration and so follows the same set of credentials-searching
strategies that AWS CLI and other AWS SDK applications would follow.

We learned this only after having already merged that upgrade, so this is
a retroactive documentation and changelog update to describe the change.
Since go-getter is now delegating this whole question to the AWS SDK, our
future upgrades of the AWS SDK will automatically adopt any upstream
changes to the default credentials chain and so our documentation about
this is now more general than before: the intention is that our users can
generally assume that OpenTofu should support everything that is documented
as supported for the AWS CLI, instead of us listing out an explicit search
sequence that will be long and inevitably become outdated again.

Signed-off-by: Martin Atkins <mart@degeneration.co.uk>

website/docs/language/modules/sources.mdx

@@ -452,13 +452,10 @@ The resulting object must be an archive with one of the same file
 extensions as for [archives over standard HTTP](#fetching-archives-over-http).
 OpenTofu will extract the archive to obtain the module source tree.
 
-The module installer looks for AWS credentials in the following locations,
-preferring those earlier in the list when multiple are available:
-
-- The `AWS_ACCESS_KEY_ID` and `AWS_SECRET_ACCESS_KEY` environment variables.
-- The default profile in the `.aws/credentials` file in your home directory.
-- If running on an EC2 instance, temporary credentials associated with the
-  instance's IAM Instance Profile.
+The module installer searches for AWS credentials in a similar way to AWS CLI,
+and so you should not typically need any additional configuration to use S3
+module sources as long as AWS CLI on your system would be able to access the
+same S3 objects.
 
 ## GCS Bucket