A different host can be specified with (undocumented, private)
NM_CLOUD_SETUP_GCP_HOST environment variable.

A different host can be specified with (undocumented, private)
NM_CLOUD_SETUP_AZURE_HOST environment variable.

The routes in iproutes were leaked (and ownership stolen
in _nmc_mangle_connection(), leaving dangling pointers).

Fix that by using a GPtrArray instead.

The (allow-none) annotation is deprecated since a long time now, it is better to
use (nullable) and/or (optional) which clarifies what it means with the (out)
annotation.

https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/1551

https://bugzilla.redhat.com/show_bug.cgi?id=2179718

Fixes: 8b7e12c2d631 ('cloud-setup/ec2: start with requesting a IMDSv2 token')
Fixes: cd74d7500278 ('cloud-setup: make nm_http_client_req() accept a method argument')

The idea is to have useful and correct helper functions, that are
generic and reusable.

nmcs_utils_poll() was done with that intent, and it is a generally
useful function. As the implementation shows, it's not entirely trivial
to get all the parameters right, when it comes to glib-integration
(GMainContext and GTask) and polling.

Whether something like a generic poll helper is a useful thing at all,
may be a valid question. E.g. you need several hooks, and the usage is
still not trivial. Regardless of that, "nm-cloud-setup-utils.c" already
had such a helper. This is only about moving it to a place where it is
actually accessible to others.

And, if it turns out to be a good idea after all, then somebody else
could use it.

nmcs_utils_poll() calls nmcs_wait_for_objects_register(), which is
specific to nm-cloud-setup.

nmcs_utils_poll() should move to libnm-glib-aux, so it should not have a
direct dependency on nm-cloud-setup code. Add instead a hook that the
caller can use for registering the object.

@probe_start_fcn is not called the first time synchronously. Fix the comment.
While at it, reword a bit.

nmcs_utils_poll() accepts two different user-data. One is passed to the
probe callbacks (and returned by nmcs_utils_poll_finish()). The other
one is passed to the callback.

Having separate user data might be useful. It's not useful for
nm_http_client_poll_req(), which both passes the same.

It's confusing to pass the same data as different user-data. Don't do
that. Use only one way.

The present version of the EC2 metadata API (IMDSv2) requires a header
with a token to be present in all requests. The token is essentially a
cookie that's not actually a cookie that's obtained with a PUT call that
doesn't put anything. Apparently it's too easy to trick someone into
calling a GET method.

EC2 now supports IMDSv2 everywhere with IMDSv1 being optional, so let's
just use IMDSv2 unconditionally. Also, the presence of a token API can
be used to detect the AWS EC2 cloud.

https://bugzilla.redhat.com/show_bug.cgi?id=2151986