DAL/Node: use labels for event emission

What

Use labels for event emission in the DAL node.

Why

Because otherwise we could easily mix the order and spawn misleading information, as I did in !16469 (merged)

How

For each event x, define a function emit_x. For instance,

let resolved_bootstrap_points =
  declare_2
    ~section
    ~name:"resolved_bootstrap_points"
    ~msg:
      "DNS resolution of {domainname} returned {number} bootstrap IP addresses"
    ~level:Notice
    ("domainname", Data_encoding.string)
    ("number", Data_encoding.int31)

gives the following

let emit_resolved_bootstrap_points  ~domainname ~number  = emit resolved_bootstrap_points (domainname, number)

Manually testing the MR

Compiling is enough.

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR