Multitenancy: expose agent configuration settings on a per-tenant basis

[esune]

When using an agent running on a multi-tenant instance of ACA-Py, each tenant might want/need to specify a different behaviour.
A lot of the the ACA-Py startup parameters/environment variables would benefit from being configurable at a tenant level (all of the "auto" flags for once). The following is a subset of settings that was identified as it is currently used across agent deployments for BCGov (see bcgov/traction#547):

• ACAPY_LOG_LEVEL
• ACAPY_INVITE_PUBLIC
• ACAPY_PUBLIC_INVITES
• ACAPY_AUTO_ACCEPT_INVITES
• ACAPY_AUTO_ACCEPT_REQUESTS
• ACAPY_AUTO_PING_CONNECTION
• ACAPY_MONITOR_PING
• ACAPY_AUTO_RESPOND_MESSAGES
• ACAPY_AUTO_RESPOND_CREDENTIAL_OFFER
• ACAPY_AUTO_RESPOND_CREDENTIAL_REQUEST
• ACAPY_AUTO_VERIFY_PRESENTATION
• ACAPY_NOTIFY_REVOCATION
• ACAPY_AUTO_REQUEST_ENDORSEMENT
• ACAPY_AUTO_WRITE_TRANSACTIONS
• ACAPY_CREATE_REVOCATION_TRANSACTIONS

Settings that are set as part of the main/agency agent startup command would likely be used as defaults, but each tenant would/should be able to override them based on specific needs.

Note: one setting that might require extra attention is the one related to the writable ledger. See #2168 for related information.