feat: add support for IAM/STS credentials management

[liramon1]

Problem

IAM credentials management is currently unsupported in the identity LSP and cannot be used in the agent codewhisperer bundle.

Solution

This feature is split into multiple PRs (in order):

1. feat(identity): add support for IAM profile management #1845
2. feat(identity): add support for retrieving IAM user credentials #1869
3. feat(identity): add STS credential management #1846

Each PR will be merged into feature/flare-iam-base, which will be merged into branch main at the end.

These changes will allow the identity LSP to load and save IAM credentials to the shared config, generate STS credentials from role assumption, and cache/invalidate/refresh STS credentials.

This feature will also contain a major refactor of the CodeWhisperer LSP to switch between consuming IAM and bearer credentials at runtime (coming soon).

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.