libtls: Client receives and processes server ServerHello message

[ryru]

Aufwandschätzung: soll=20 Stunden

The server says "Hello" back. The server provides information including the following:

• server random data (used later in the handshake)
• a selected cipher suite
• a public key for key exchange
• the negotiated protocol version

Two server responses must be differentiated: choose TLS legacy or TLS 1.3 code path

• [x] handle server random data (used later in the handshake) planned 4h
• [x] handle a selected cipher suite planned 4h
• [x] handle a public key for key exchange planned 4h
• [x] handle the negotiated protocol version planned 4h
• [x] handle lagacy TLS responses planned 4h

Consider:

• 4.1.3. Server Hello