feat: Support TLS config

[jopemachine]

Resolves #18.

• Support for TLS encrypted network connections between RaftNodes
• Refactoring of code to generate Config using ConfigBuilder

How to test

After executing the following command, enable the TLS feature in the example code's cargo.toml and bootstrap the cluster.

openssl genrsa -out server.key 2048 ; \
echo "[ req ]
default_bits       = 2048
default_md         = sha256
default_keyfile    = server.key
distinguished_name = req_distinguished_name
req_extensions     = req_ext
x509_extensions    = v3_req
prompt             = no

[ req_distinguished_name ]
C  = KR
ST = Seoul
L  = Seoul
O  = MyOrganization
OU = MyUnit
CN = localhost

[ req_ext ]
subjectAltName = @alt_names

[ v3_req ]
subjectAltName = @alt_names

[ alt_names ]
DNS.1 = localhost
IP.1  = 127.0.0.1" > openssl.cnf ; \
openssl req -new -key server.key -out server.csr -config openssl.cnf ; \
openssl x509 -req -days 365 -in server.csr -signkey server.key -out server.crt -extensions v3_req -extfile openssl.cnf ; \
cp server.crt ca_cert.pem