Add support for adding custom templates

[leic4u]

The nginx configuration template is a nice and helpful feature.

But if I have some configurations that need to be used frequently and not included in temlplates, it is inconvenient.

How about support users manage thier own configuration templates?

It will be a great feature that makes nginx config simple and fastly.

[jearton]

+1

[xe5700]

+1