Add support for TF automatic execution without manual approval supporting dev workflows

[gberche-orange]

Is your feature request related to a problem? Please describe.

As a template author, I'm always frustrated when make some TF spec changes, because I need to perform many time consuming actions to get results (see precise description into #22).

In particular when doing broker developments such as COAB, I'd expect automatic broker registration updates (so that catalog refreshes in marketplace) without manual approval: in broker development mixing cf-app support (for broker push and smoke tests) and TF (for broker registration), a lack of TF application leads to Cf app smoke test failures (e.g. catalog does not refresh in CF marketplace)

Describe the solution you'd like

A way to:

• turn off manual approval of the TF specs per deployment/root-deployment
• trigger on incoming changes (such as a new version of a broker artefact in a github release) or increase frequently of TF spec application (currrently check consistency is scheduled once at noon)

Describe alternatives you've considered

• broker registration update duplicated in cf app post deploy script (in addition to TF specs)
• a cron job on my desktop which periodically gives manual TF validation
• moving broker cf app push to TF which reduces synchronization between cf app and TF specs application.

[o-orand]

Terraform plan is executed on the fly, on each change, but OPS still need to manual approve change (ie terraform apply).