[ upstream commit d3ad556 ]

According to the documentation of the flag `endpoint-regen-interval`, the
periodic endpoint regeneration should only be configured if the interval
is bigger than `0`.

```
Periodically recalculate and re-apply endpoint configuration. Set to 0 to disable
```

But the current implementation has 2 issues.

* If the interval is configured as `0`, the regeneration is executed once at startup
* If the endpoint garbage collection is disabled, the periodic regeneration isn't
  configured at all.

This commit fixes these two issues by splitting the controller registrations
and only apply them if their interval is bigger than `0`.

Note: Always executing the stop hook that removes the controllers isn't a problem.
      Even if no controller would be registered.

Signed-off-by: Marco Hofstetter <marco.hofstetter@isovalent.com>
Signed-off-by: Marco Iorio <marco.iorio@isovalent.com>

[ upstream commit ae1e694 ]

[ backporter's notes: hit minor conflict in `pkg/endpoint/restore_test.go`
  due to changes in surrounding context, resolved accepting combination. ]

In the past, the metric `agent_bootstrap_seconds` with label
`scope=restore` was used to publish some endpoint restoration
related metrics.

With the modularization of the legacy daemon init logic, some of the
endpoint restoration logic no longer reported its duration to that metric.

In addition to this, the label `scope=restore` was pretty generic, because
other restoration logic was using the same label (e.g. identity restoration).
And the metric didn't take into account that the actual regeneration of
the restored endpoints was executed asynchronously.

To shed some more light into the endpoint restoration process, this
commit introduces two endpoint restoration specific metrics.

* `endpoint_restoration_endpoints` - with label `phase` & `outcome`
* `endpoint_restoration_duration_seconds` - with label `phase`

The following phases of the endpoint restoration process report the metric.

* `read_from_disk`: Reads old endpoints from state dir
* `restoration`: Restore old endpoints. includes validation & IP re-allocation
* `prepare_regeneration`: Trigger asynchronous regeneration
* `initial_policy_computation`: Duration until the initial policy for all restored endpoints is computed
* `regeneration`: Duration until all restored endpoints are regenerated

e.g.

```
root@kind-control-plane:/home/cilium# cilium-dbg shell metrics endpoint_restoration
Metric                                         Labels                                                Value
cilium_endpoint_restoration_duration_seconds   phase=initial_policy_computation                      0.006262
cilium_endpoint_restoration_duration_seconds   phase=prepare_regeneration                            2.506187
cilium_endpoint_restoration_duration_seconds   phase=read_from_disk                                  0.002105
cilium_endpoint_restoration_duration_seconds   phase=regeneration                                    2.270423
cilium_endpoint_restoration_duration_seconds   phase=restoration                                     0.101983
cilium_endpoint_restoration_endpoints          outcome=failed phase=read_from_disk                   0.000000
cilium_endpoint_restoration_endpoints          outcome=failed phase=regeneration                     0.000000
cilium_endpoint_restoration_endpoints          outcome=failed phase=restoration                      1.000000
cilium_endpoint_restoration_endpoints          outcome=skipped phase=restoration                     1.000000
cilium_endpoint_restoration_endpoints          outcome=successful phase=initial_policy_computation   4.000000
cilium_endpoint_restoration_endpoints          outcome=successful phase=prepare_regeneration         4.000000
cilium_endpoint_restoration_endpoints          outcome=successful phase=read_from_disk               6.000000
cilium_endpoint_restoration_endpoints          outcome=successful phase=regeneration                 4.000000
cilium_endpoint_restoration_endpoints          outcome=successful phase=restoration                  4.000000
cilium_endpoint_restoration_endpoints          outcome=total phase=initial_policy_computation        4.000000
cilium_endpoint_restoration_endpoints          outcome=total phase=prepare_regeneration              4.000000
cilium_endpoint_restoration_endpoints          outcome=total phase=read_from_disk                    6.000000
cilium_endpoint_restoration_endpoints          outcome=total phase=regeneration                      4.000000
cilium_endpoint_restoration_endpoints          outcome=total phase=restoration                       6.000000
```

Signed-off-by: Marco Hofstetter <marco.hofstetter@isovalent.com>
Signed-off-by: Marco Iorio <marco.iorio@isovalent.com>