Automatically apply dashboard yamls on boot

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__Proposal:__
Is it possible to mount in a couple dashboard yml/jsons (like this https://github.com/influxdata/influxdb/blob/master/pkger/testdata/dashboard.yml) and apply them on boot for influxdb v2? We're running influxdb v2 on k8s and ideally would like to have a couple dashboards pre-configured. It doesn't seem like this is possible right now (we would need to hop into the container and run a `influx apply -f` after the server has started) but maybe a flag on the `influxd` entrypoint would make sense?

__Current behavior:__
Dashboards in the form of yml/jsons must be explicitly applied

__Desired behavior:__
Be able to mount in a directory of yml/jsons and have the dashboards pre-configured on boot.

__Use case:__
We're a 3rd party software deploying onto a k8s system. We're planning on shipping software with a fully-featured metrics stack with influxdb (and ideally pre-configured chronograf dashboards).

Start with the influxd entrypoint and the existing `influx apply -f` workflow, using the linked dashboard.yml as the input example. Determine how a mounted directory of dashboard YAML/JSON files could be discovered and applied during boot; done means dashboards are pre-configured without running a separate command after startup.

Written by the indexing model from the issue text.