CouchDB support for non-admin account

[jceb]

Currently, the couchdb store can't operate with a non-admin account.

I found the following issues that hold back the couchdb store:

1. The _users database is queried. This feature has been disabled in version 3.1.0 Non-Admin users are unable to read their own user doc in 3.1.0 apache/couchdb#3084
2. Requested stores are directly created without testing their existence. The subsequent error message is that there's a lack of permissions https://github.com/hyperledger/aries-framework-go-ext/blob/main/component/storage/couchdb/store.go#L373