Add function to get SDK and Lang version

[shaobo-he-aws]

Description of changes

Issue #, if available

Checklist for requesting a review

The change in this PR is (choose one, and delete the other options):

• [x] A backwards-compatible change requiring a minor version bump to cedar-policy (e.g., addition of a new API).

I confirm that this PR (choose one, and delete the other options):

• [x] Updates the "Unreleased" section of the CHANGELOG with a description of my change (required for major/minor version bumps).

I confirm that cedar-spec (choose one, and delete the other options):

• [x] Does not require updates because my change does not impact the Cedar formal model or DRT infrastructure.

I confirm that docs.cedarpolicy.com (choose one, and delete the other options):

• [x] Does not require updates because my change does not impact the Cedar language specification.

[john-h-kastner-aws]

If we want this function (as opposed to a function returning the lang version). We should be able to get the SDK version from env vars to avoid the need for a manual update on every release.

• CARGO_PKG_VERSION — The full version of your package.
• CARGO_PKG_VERSION_MAJOR — The major version of your package.
• CARGO_PKG_VERSION_MINOR — The minor version of your package.
• CARGO_PKG_VERSION_PATCH — The patch version of your package.
• CARGO_PKG_VERSION_PRE — The pre-release version of your package.

This information should also be available to Cedar consumers from their Cargo.lock file (using this crate), so I'm not sure I see the need for this. Cedar langauge version on the other hand is something only that can only be known if we explicitly report it.

[shaobo-he-aws]

Can you add a function to the CLI to get the version number?

Yes, working on it.

[shaobo-he-aws]

Can you add a function to the CLI to get the version number?

Done.