nrpe_relation_joined should ensure the vector binary is present

[lucabello]

Bug Description

The relation between cos-proxy and nrpe is not sufficient for logs to reach Loki when related to it cross-model. The reason for this is that vector doesn't start when the nrpe relation is joined. Adding filebeat to the model makes vector start successfully.

To address this bug, modify _nrpe_relation_joined() so that it ensures the vector binary is there, the same way it's done for _filebeat_relation_joined().

To Reproduce

machine model

1. juju deploy ubuntu
2. juju deploy nrpe
3. juju deploy cos-proxy
4. juju relate nrpe ubuntu
5. juju relate cos-proxy nrpe

k8s model

1. juju deploy cos-lite --channel=edge
2. cross-model relate cos-proxy to loki

Environment

∮ microk8s version
MicroK8s v1.26.1 revision 4596
∮ juju --version
3.1.0-genericlinux-amd64
∮ lxd --version
5.12

Relevant log output

-

Additional context

No response