New port: sysutils/gomplate

Gomplate is a template-based CLI tool. gomplate supports additional
template datasources such as: JSON, YAML, AWS EC2 metadata, BoltDB,
sockaddr, Hashicorp Consul, and Hashicorp Vault secrets.

Gomplate lets you process templates which also include shell-like
variables. Also there are some useful built-in functions that can be
used to make templates even more expressive.

Reviewed by: swills, mat
Approved by: swills (mentor)
Differential Revision: https://reviews.freebsd.org/D15327