Feature: Add automated comment in PRs when `static-builds.yml` succeeded

[erikmd]

Related user(s):

@erikmd

Related issue(s) or PR(s):

• Issue https://github.com/ocaml-sf/learn-ocaml/issues/475
• & PR https://github.com/ocaml-sf/learn-ocaml/pull/501

Related project scope(s):

other

The problem:

The pin-artifacts.yml workflow just adds the perennial artifacts URLs to commit statuses, which is handy but not optimal in the case of PRs' UX.

Wanted solution:

It would be good to extend pin-artifacts.yml to also add a unique bot comment in the opened PR:

• mentioning the artifacts URLs;
• summarizing the installation procedure.
• cf. my answer in this thread

Considered alternatives:

No response

Additional context:

No response