Implement Vault for secret management and key rotation

[i5okie]

Inventory of Credentials

Notes added after initial assessment

Secret Name	Rotatable Keys	Type	Instances	Notes
vc-authn-oidc-agent		vc-authn-oidc-agent pods
vc-authn-controller		controller key	vc-authn pods	potentially controller-api-key
vc-authn-database	admin-password, database-password	pg credential	vc-authn, vc-authn pg pods
vc-authn-oidc-acapy-secret		agent keys	vc-authn-oidc-agent pods	potentially adminApiKey, walletKey
]
vc-authn-oidc-api-key		controller key	vc-authn-oidc pods	potentially controllerApiKey
vc-authn-oidc-mongodb	mongodb-passwords, mongodb-replica-set-key, mongodb-root-password	mongo credentials	vc-authn-oidc pods, vc-authn mongodb pods
vc-authn-oidc-postgresql	admin-password, database-password	pg credentials	vc-authn agent pods, vc-authn pg pods