[TruffleHog] Add macOS Keychain as a secret scanning source

Please review the [Community Note](https://github.com/trufflesecurity/trufflehog/blob/main/.github/community_note.md) before submitting Is this something in scope of trufflehog? ## Description Some tools store credentials in macOS Keychain in an unsafe way by using the `security` tool. This allows any other process to read this credential without any user prompt. Create a secret: ```sh security add-generic-password \ -a "test-account" \ -s "trufflehog-test-service" \ -w "super-secret-value" \ -U ``` Enumerate secrets readable by `security` (takes a long time): ```sh security dump-keychain -a | less # search for /usr/bin/security ``` Read the secret: ```sh security find-generic-password -a test-account -g ``` ``` # ... # password: "super-secret-value" ``` ### Preferred Solution Ideally a new trufflehog source: 1. Enumerate all unlocked macOS keychains. 2. Enumerate all readable secrets in each keychain. 3. Read each secret and pass it