Create KeyManagementProvider or a new key/cert fetch component

[binbin-li]

Is your feature request related to a problem?

In Ratify v1, we have KeyManagementProvider to fetch and save certs/keys from remote key vaults or inline template. In v2, we should have a similar component to serve this functionality.

What solution do you propose?

n/a

What alternatives have you considered?

n/a

Any additional context?

No response