Use a single binary to run the different Operator processes

[lrgar]

We currently run three containers with the Operator package,

• The good old Operator itself.
• The webhook bootstrapper.
• The webhook server.

I initially created one binary for each one of these, but we can merge them into a single binary, and use a subcommand to run it on any of these modes. The difference between them is which reconcilers are started.

I'm calling the subcommands respectively,

• operator
• webhook-bootstrapper
• webhook-server

So, if you run the Operator locally, it would be like,

$ operator-sdk run --local --operator-flags="operator"
$ WATCH_NAMESPACE=dynatrace go run ./cmd/manager/ -- operator

Finally, I'm removing the add_***.go files that are created by the operator-sdk's scaffolding, and instead using a list on cmd/manager/operator.go. The idea here is that we don't really use scaffolding and just copy/paste for new reconcilers, and having a simple list is more clear than depending on the behavior of init() functions. The webhook processes are already just adding specific reconcilers, so we would get some consistency.

[lrgar]

Now using operator as the default subcommand if nothing is set. You need to explicitly use the subcommand to run the webhook server and bootstrapper.