Reducing verbosity of various logs (#3664)

## Motivation and Context
<!--- Why is this change required? What problem does it solve? -->
<!--- If it fixes an open issue, please link to the issue here -->
Our logs had several entries that were extremely verbose and made them
harder to sort through. This change aims to reduce the verbosity of
those logs to something more manageable.

## Description
<!--- Describe your changes in detail -->
- Removed the logging of the full IMDS Client struct, replaced with a
message that it was truncated
- Removed logging the full `Configbag` in a couple places in
`RuntimeComponentsBuilder`
- Removed logging of full `ProvideCredentials` objects in the
CredentialsProviderChain` and replaced with just their names

There are some verbose logs I did not remove because I was not sure of
their usefulness. Most notably the `PartitionResolver` struct logs
several hundred lines of region information each time it appears. Happy
to truncate that as well if those logs aren't too helpful.

## Testing
<!--- Please describe in detail how you tested your changes -->
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to -->
<!--- see how your change affects other areas of the code, etc. -->
This was tested locally by running the SDK [logging
example](https://docs.aws.amazon.com/sdk-for-rust/latest/dg/logging.html)
code with `RUST_LOG=trace` prepended to the `cargo run` command. For
comparison, when saved as a .txt file, the old logs take up `2.8MB` and
the new logs take `273KB` for the same operation.

## Checklist
<!--- If a checkbox below is not applicable, then please DELETE it
rather than leaving it unchecked -->
- [x] I have updated `CHANGELOG.next.toml` if I made changes to the
smithy-rs codegen or runtime crates

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