refactor(pkg/server): tls configuration is moved in command package from server

[mmeloni]

Tls configuration is moved inside command package.
Immudb ux now is the follow:

if certificate and pkey are provided they are injected in tls config

if mtls flag is provided certificate authority is mandatory and can be provided with --clientcas flag.

Example on how to setup mtls between immudb and immuclient:

Generate ssl artifacts with

./tools/mtls/generate.sh localhost secretpassword

Launch immudb :

./immudb --mtls --pkey ./tools/mtls/3_application/private/localhost.key.pem --certificate ./tools/mtls/3_application/certs/localhost.cert.pem --clientcas ./tools/mtls/2_intermediate/certs/ca-chain.cert.pem

Launch immuclient with:

./immuclient --mtls --servername localhost --pkey ./tools/mtls/4_client/private/localhost.key.pem --certificate ./tools/mtls/4_client/certs/localhost.cert.pem --clientcas ./tools/mtls/2_intermediate/certs/ca-chain.cert.pem login immudb

[coveralls]

Coverage decreased (-0.0007%) to 87.517% when pulling ff20bdc on chore/expose-tls into 0d3d91e on master.