feat: expose timeouts

[UnicornChance]

Description

A request was made so that we can expose the keycloak timeouts to be overridden for demo purposes. Update exposes access token lifespan and sso session idle timeout. To be clear, these values still maintain the same defaults and uds-core will not be updating the values we use out of the box in our bundles.

Add the exposed environment variables in the example customization doc as well.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Other (security config, docs update, etc)

Checklist before merging

• Test, docs, adr added or updated as needed
• Contributor Guide Steps(https://github.com/defenseunicorns/uds-template-capability/blob/main/CONTRIBUTING.md#submitting-a-pull-request) followed