This tries to make the same functions emit and consume the same type of
data all over the application.
If a function transform data, it should emit new data, not a pointer.
This commit adds some Prometheus metrics to /metrics in headscale.
It will add the standard go metrics, some automatic gin metrics and some
initial headscale specific ones.
Some of them has been added to aid debugging #97 (loop bug)
In the future, we can use the metrics to get rid of the sleep in the
integration tests by checking that our expected number of nodes has been
registered:
```
headscale_machine_registrations_total
```
This commit moves toNode to the bottom of the file, and adds a helper
function for lists of Machines to be converted.
It also adds string helpers for Machines and lists of machines.
Lastly it splits getPeers into getDirectPeers, which exist in the same
namespace, and getShared, which is nodes shared with the namespace.
getPeers is kept as a function putting together the two lists for
convenience.
This commit rewrites a bunch of the code to always use *Machine instead
of a mix of both, and a mix of tailcfg.Node and Machine.
Now we use *Machine, and if tailcfg.Node is needed, it is converted just
before needed.
This function migrates more poll functions (including keepalive) to
poll.go to keep it somehow in the same file.
In addition it makes changes to improve the stability and ensure nodes
get the appropriate updates from the headscale control and are not left
in an inconsistent state.
Two new additions is:
omitpeers=true will now trigger an update if the clients are not already up
to date
keepalive has been extended with a timer that will check every 120s if
all nodes are up to date.
