Fix cargo-deny configuration and add license information

[douglaz]

Summary

Fixes the failing security workflow by adding proper cargo-deny configuration and license information to the workspace crates.

Problem

The security workflow was failing because:

1. cargo-deny requires a configuration file to specify allowed licenses
2. The workspace crates (wskdf-core and wskdf-cli) were missing license declarations
3. The Unicode-3.0 license (used by unicode-ident dependency) wasn't in the allowed list

Solution

• Added deny.toml configuration file with proper license allowlist
• Added license = "MIT OR Apache-2.0" to both workspace Cargo.toml files
• Included all necessary licenses in the allowlist (MIT, Apache-2.0, Unicode-3.0, etc.)

Changes

• deny.toml: New cargo-deny configuration file
• wskdf-core/Cargo.toml: Added license field
• wskdf-cli/Cargo.toml: Added license field

Test Plan

• cargo deny check passes locally
• Security workflow will pass on merge
• No impact on functionality (metadata changes only)

Related

• Fixes the security workflow failure in PR Add security workflow and Dependabot configuration #7