entrypoints=0.3 rquires flit as build backend

pkgconfig=1.5.1 requires poetry as build backend.

Earlier version 1.22.0 does not support recent setuptools.

Latest version 1.26.2 has more complex build requirements,
left for later.

Now that buildout uses pip to correctly follow pyproject.toml,
cattrs=22.2.0 requires poetry as the build backend.

For now it's easier to install as wheel than to install poetry and
then use it as setup-egg for cattrs. This must be done eventually.

zc.buildout=2.7.1+slapos020 is SlapOS-patched buildout2 with support
for bootstrapping buildout3, required to be able to install buildout3.

Downgrade related eggs to pre-buildout3 versions as well.

Version up zc.buildout, pip and zc.recipe.egg.

Version up slapos.rebootstrap to adapt to buildout3.

@jerome reports ue/cell/* schemas are not valid JSON and he is right: in
30179be5 I made a mistake to add extra trailing " after propertyOrder
integer value. Fix that.

See merge request !1564

  They are json-editor specific features and are not part of the json schema

  By using ref to ../ru/input-schema.json you append oneOf list and dont extend the
  current list.

  This fixes validation properly when oneOf the values are used.

  Done by Thomas Gambier

See merge request nexedi/slapos!1555

See commit 77eabe12.

BTW, the mentionned 3ff25131
commit was part of !1559.

See merge request nexedi/slapos!1549

* Separate root and subscriber from drone SRs to avoid compilation of unnecessary dependencies
* display logs in debug mode

Rename subinstances to avoid conflict. Once a subinstance is allocated on a
computer, changing `sla-computer_guid` does not move the subinstance. Therefore
an instance name containing the computer's guid is necessary.

Fix logs printed out of the logging area

Process all available logs to avoid delay in log printing.

Indicate the time of the last received message in format hh:mm:ss .

Set c-astral SR in its own file and leave the autopilot used blank in software-base.cfg

Set publishing interval to 200 ms so radio network is not overflown

Allow subscribers' network interface to be different from the drones' one

* use the default RSA key length, instead of hardcoding 1024 (too weak) or 2048 (same as the current default).
* use SHA256 in certificates.