DAL: Allow slot publication from the DAL node

What

Instruct the DAL node to publish DAL commitment on the Layer 1 network and add an option --publish-slots-regularly FREQUENCY-SLOT-SECRET_KEY which emits a publication every FREQUENCY level on slot index SLOT signed with SECRET_KEY.

Why

Because, when tezt-cloud experiments involve a lot of machines, the orchestrator is overwhelmed and miss a lot of publication orders. This aims at lightning the burden on the orchestrator by letting the producer DAL nodes deal of publications by themselves.

How

Since this is mainly useful for tests, the new command line option --publish-slots-regularly is only accessible if the environment variable TEZOS_DAL_PUBLISH_REGULARLY_I_KNOW_WHAT_I_AM_DOING is set to yes.

Manually testing the MR

One should be able to launch a L1 node on any test network and then:

TEZOS_DAL_PUBLISH_REGULARLY_I_KNOW_WHAT_I_AM_DOING=yes ./octez-dal-node run --observer 20 --publish-slots-regularly 1-20-YOUR_SECRET_KEY

and then observe that you indeed publish at every level on slot 20.

It requires the account related to provided secret key to be funded and revealed on targeted network.