Support TLS client session cache

[masnax]

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@cole-miller pointed me to https://pkg.go.dev/crypto/tls#ClientSessionCache which might be useful in reducing the TLS connection overhead that contributes to the go-dqlite performance issues that we see.

As such, this introduces an LRU cache of size 64, which was chosen as it's the default size if 0 is passed instead, when initializing the cache.

I haven't tested its efficacy yet, so it's just a draft for now.