Use keySeed for zcaps instead of clientSecret.

[aljones15]

• Solves a naming issue where the same name was being used for oauth2 client secrets as for zcap key seeds.
• [x] Awaits all test projects update to use keySeed for zcap endpoints.

Addresses: https://github.com/w3c-ccg/vc-api-test-suite-implementations/issues/2

Add KEY_SEED_DB and modify the github action workflow:

• [x] https://github.com/w3c-ccg/di-eddsa-2022-test-suite/settings/secrets/actions/new
• [x] https://github.com/w3c-ccg/status-list-2021-test-suite/settings/secrets/actions
• [x] https://github.com/w3c-ccg/vdl-test-suite/settings/secrets/actions
• [x] https://github.com/w3c-ccg/vc-api-verifier-test-suite/settings
• [x] https://github.com/w3c-ccg/vc-api-issuer-test-suite/settings
• [x] https://github.com/w3c-ccg/di-ed25519-test-suite/settings