add hostname as prom label for cardinality

[Issif]

What type of PR is this?

Uncomment one (or more) /kind <> lines:

/kind bug

/kind cleanup

/kind design

/kind documentation

/kind failing-test

/kind feature

Any specific area of the project related to this PR?

Uncomment one (or more) /area <> lines:

/area build

/area config

/area outputs

/area tests

What this PR does / why we need it:

Fix cardinality issue with Prometheus metrics

2023/03/21 13:14:00 http: panic serving 127.0.0.1:46890: inconsistent label cardinality: expected 9 label values but got 10 in prometheus.Labels{"bkey":"BValue", "ckey":"CValue", "fd_name":"", "hostname":"falco-rkvpv", "k8s_ns_name":"falco1", "k8s_pod_name":"falco-rkvpv", "priority":"Notice", "proc_name":"bash", "rule":"Terminal shell in container", "user_name":"root"}

Which issue(s) this PR fixes:

Bug introduced by #420

Fixes #

Special notes for your reviewer:

[Issif]

cc @Lowaiz

[poiana]

LGTM label has been added.

Git tree hash: f255ea6c8cb1a4a8f60be3991dade0bd6a986322

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fjogeleit, Issif

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [Issif,fjogeleit]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment