Add workflows to manually/weekly update the runtime lockfiles and the SDK lockfile (#3844)

## Motivation and Context
This PR introduces GitHub workflows to automate the process of running
`cargo update` on lockfiles and creating PRs in this repository.
- Scheduled workflow: This workflow runs weekly to ensure dependencies
are updated to the latest semver-compliant versions.
- Manual workflow: This workflow provides the same functionality but can
be triggered on-demand. It includes an option to force updates on [known
broken
dependencies](https://github.com/smithy-lang/smithy-rs/blob/6b42eb5ca00a2dc9c46562452e495a2ec2e43d0f/aws/sdk/build.gradle.kts#L503-L504).

## Testing
- Did NOT run a scheduled workflow, assuming that's a thin wrapper
around what has been verified. We can afford a "see what happens and fix
if necessary" approach once this PR is merged into main.
- Manually triggered a workflow, successfully opening PRs with updated
lockfiles ([ex1](https://github.com/smithy-lang/smithy-rs/pull/3842),
[ex2](https://github.com/smithy-lang/smithy-rs/pull/3843)).
- Manually triggered a workflow, forcing updates on broken dependencies
(didn't open a PR to avoid noise, but confirmed `minicbor` was [updated
to
0.24.4](https://github.com/smithy-lang/smithy-rs/blob/088cbe9f52695be0b24f4d0941667cf29631e785/rust-runtime/Cargo.lock#L2245-L2246)).

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