Add a Trusted Platform Module Provider

[hug-dev]

This issue tracks the work of adding a new provider in PARSEC for TPM support. This new provider will implement the Provide trait to respond to clients requests.

Multiple options are possible for the implementation:

• produce a FFI to one of the TPM2 Software Stack API interfaces and dynamically link to a library implementing it (path provided in the configuration). Ideally we want to use the highest abstraction level (Feature API) but it seems to be work in progress. The highest level API we can use today is the Enhanced System API.
• investigate the use of the tss-sapi crate, to see if it would fit our needs
• investigate the use of a PKCS 11 to TPM 2 bridge. At a first glance, the README files warns that it is not production ready though.

cc @parallaxsecond/maintainers

[hug-dev]

From the ESAPI specs:

No two threads are allowed the same ESAPI context simultaneously.

We did a test where creating two contexts and trying in one to refer to the key handle of the other, ESAPI does not allow that (key handle does not exist) (cc @ionut-arm ).
That would mean that inside the provider functions, the code will be single-threaded (ensured with mutexes) so that we only have one context at all time. This context will be created when the provider is created.

[hug-dev]

#75 was just merged :)