[feature request] optional https launch flag

[Zydnar]

To use or test https server, see: https://reactphp.org/socket/#secureserver

[jdomenechb]

I'm thinking of using environment vars to satisfy this feature. Given the fact that, looking at the documentation, the local_cert parameter seems to be required, I would suggest using the following environment vars:

REACTPHPSVR_SSL_LOCAL_CERT='xxxx' # If defined, SecureServer is used
REACTPHPSVR_SSL_PASSPHRASE='xxxx' # Optional
REACTPHPSVR_SSL_CRYPTO_METHOD='STREAM_CRYPTO_METHOD_TLSv1_2_SERVER' # Optional, using name of constant to simplify readibility