Add support for unnamed EC

[manison]

Describe the feature
Currently the provider only supports standard named elliptic curve objects. This feature would allow loading EC keys with nonstandard EC parameters.

Expected behavior
The provider is loading EC keys with nonstandard EC parameters.

Additional context
Currently we use libp11 engine and OpenSSL 1.1 to work with our custom EC. We would like to migrate to OpenSSL 3 and this provider but this missing feature is one of the things that prevent us to migrate. I would try to prepare PR. Would this feature be accepted?

[simo5]

Custom EC curves can be very dangerous. I am also not aware of modules that allow to load custom curves. I might accept a patch that gates this behind a config option though.

[simo5]

@manison are you going to provide a PR for this?

[manison]

I would like to. Now I have some work-in-progress that needs heavy polishing and I'm struggling with integrating into test suite.