ghost: ability to provide a custom mail name

ghost/Dockerfile

@@ -15,6 +15,8 @@ ENV GHOST_NODE_VERSION_CHECK=false \
     SMTP_PASS=12345 \
     SMTP_USER=user \
     SMTP_PORT=666 \
+    SMTP_SENDER_MAIL=user@domain.tld \
+    SMTP_SENDER_NAME=Ghost \
     ENABLE_ISSO=False \
     ISSO_HOST=isso.domain.tld \
     ISSO_AVATAR=false \