Request adding 'action' for templates to specify using 'reload_signal' or 'kill_signal'

We actually use consul-template to start consul, but only some configs are listed in the Reloadable Configuration (https://www.consul.io/docs/agent/options.html#reloadable-configuration). Specifically, we render TLS certs and the main config file to rotate actl tokens but only the TLS certs are "reloadable". The simple solution is to allow a given template to specify whether to use the 'reload_signal' or 'kill_signal' after render the template.

The current workaround seems rather complicated. We must remove the 'reload_signal' so it defaults to killing and restarting the process, but use the 'command' setting on the TLS templates which executes a script to send the HUP signal to the consul process. The script needs to know the PID so we must implement a pidfile with consul configs. Again, it would be much easier to just have consul-template be able to use the alternate signal instead.

No source files or tests are named. Start by tracing how consul-template applies the global reload_signal and kill_signal settings after rendering a template, then inspect the template configuration path; done means each template can choose either signal while existing global behavior remains unchanged.

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