Disable dependency dashboard (Closes: #3, #4).

Thus far, the renovate dependency dashboard has only solicited confusion as to its intended usefulness.

It is not necessary to make meta tickets to track MRs, since in most cases, we either already automatically auto-assign MRs, or there is already a triage process involved that will process them. We also have the ability to look for those that fall through the cracks, and adjust if and when we encounter those. As a result, this just adds an additional issue processing step that is unnecessary.

Additionally, in some teams, where there are a number of different projects underneath the team, having a dependency dashboard opened for each project starts to clutter the project quite a bit (eg. A/C).

Some projects have already disabled the dependency dashboard (cf. tpo/network-health/tor-weather!72 (merged)), while others are wondering how it is useful (cf. tpo/core/onionmasq#65 (closed)).

This commit disables this by default. If there is a strong argument that can be made that it should be enabled instead, we can re-enable it, or projects can turn it on if they find it is a useful feature.