Add command to detect when SSO credential is expired (but CLI STS token is still valid)

### Describe the feature

Need some way to detect expired SSO credentials without manually reading the cache files. This can be by implementing a dedicated command, or by making `aws sso login` optional or by allowing the cli to be run with a flag telling it to ignore the STS cache files (but still seeing SSO ones)

### Use Case

There is a very frequently encountered edge case when SSO credentials have expired but the cached STS credential for CLI is still valid, so that aws-cli still appears to work, but no other tool (example - `ecr-credentials-helper`) works.

I would like to use the cli itself to detect this rather than try to dig in the cache files - I know it is possible to do, but it gets very ugly very fast and requires a lot of code that would have to be distributed.

### Proposed Solution

* command like `aws sso status` that will return success if current SSO session exists and is valid, and error if it is not

Alternatives:

Alternative 1. `aws sso login --optional` - add `--optional` flag to `aws sso login` so that it only triggers login IF you are not already logged in.

Alternative 2. `aws --no-cache sts get-caller-identity` - add a `--no-cache` flag to aws that will ignore any STS credential caches when (no read or write) without deleting the cache

### Other Information

_No response_

### Acknowledgements

- [ ] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### CLI version used

aws-cli/2.17.39 Python/3.11.9 Darwin/24.6.0 exe/x86_64

### Environment details (OS name and version, etc.)

MacOs 15