uTLS probe

[jmwample]

Add a tls probe that can build the ClientHello out of a uTLS fingerprint. In whole addresses #6 because we could in theory send any fingerprint.

[jmwample]

The generation time for these payloads is not good, like significantly worse than Quic.

This was generated using a CPU profiling benchmark comparing TLS, Quic, and uTLS probe generation.

The probe works and generates a valid TLS ClientHello, but in calling ApplyPreset the utls.UConn has to call generateECDHEParameters twice serially. Once in makeClientHello and once directly.

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To generate the profiling information run:

# generate cpuprof
go test -bench=GeneratePayloads -cpuprofile=cpuprof/genpayload_utls.out

# view cpuprof
pprof -http :9000 cpuprof/genpayload_utls.out  

[jmwample]

better solution found. Generate one ClientHello with a call to ApplyPreset. From here we can modify the PubClientHelloMsg object to change out fields that need randomized (client Random, SessionID, ...?). This actually works really well and is faster than the original TLS probe generator.
NOTE: This required a PR to utls to add Marshal() for PubClientHelloMsg refraction-networking/utls#138

todo:

• decide what fields need swapped per probe
• make sure seeding is happening properly so subsequent probes actually contain random data
• allow client to specify the fingerprint somehow