- Move [theia] section and dependencies into component/theia
- Make [theia] section shared

Aggregate monitoring URLs from the main theia, clones and PBS.

Also add monitor-setup-url to the parameters published by the PBS.

The import script was overwriting the contents of ~/etc
which destroyed all the services running in the clone,
including the ones that allow the PBS to push new backup files.

This will force a password reset

https://github.com/eclipse-theia/theia/blob/v1.20.0/CHANGELOG.md#v1200---11252021

Adapt all promise sections to changes in plugin promise recipe.

Without this fix, selecting a completion with the keyboard is not really
possible.

With Theia 1.17.2 we remain stuck on the loading page.

This reverts commit 6103d29a.

To have the timeline view

The issue is now fixed in 1.16.0

This new version has a dependency to libsecret

Also adjust dependencies to the ones from https://github.com/eclipse-theia/theia/blob/v1.16.0/examples/browser/package.json
except api-samples which is not useful.

This introduces some breaking changes to the check_url_available
promise:

- http_code has been renamed to http-code
- check-secure = 1 has been deprecated; http-code = 401 should be used
  instead

Change all `check_port_listening` promises to `check_socket_listening`
and rename all associated `config-hostname` arguments to `config-host`

Before this commit, instance parameters that have a default null value
in JSON format were rendered as 'None' string in instance-theia.cfg.

In particular, Theia frontends were always requested with unsolvable
SLA parameters that prevented a frontend from ever being allocated:
```
sla-instance_guid = None
```

This is required for example to preview images (ie. open a .png file from the
editor). Without the default value of {{uuid}}.mini-browser.{{hostname}} is used
but we don't have anything in place to resolve such domain names.

Before this commit, the Go workspace was always activated before
launching the Theia shell and starting the embedded supervisord.

This in turn added the gcc installed by Theia to the PATH, meaning
that nested instances would be compiled with Theia's gcc instead of
the system gcc, making the compilation outcome dependant on Theia.

With this commit, the gcc resolved by PATH is now the system one.

This option takes a string representing a valid JSON object and
forwards the corresponding python dict to the embedded instance.

This defers the rendering of `instance-theia.cfg.in` to the instance
creation time instead of the software installation time, which will
allow buildout sections to be added based on the instance parameters.

See merge request !981