:fix: add publish counter for internal messages

[riccardomodanese]

Brief description of the PR.
Add a counter to count the messages published through the internal connector

Related Issue
none

Description of the solution adopted
just create a new counter in the right place

Screenshots
none

Any side note on the changes made
none

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 21.08%. Comparing base (3025da1) to head (63bd6a1).

Additional details and impacted files

@@              Coverage Diff              @@
##             develop    #4007      +/-   ##
=============================================
- Coverage      21.09%   21.08%   -0.01%     
  Complexity        10       10              
=============================================
  Files           1954     1954              
  Lines          41430    41438       +8     
  Branches        3801     3802       +1     
=============================================
  Hits            8739     8739              
- Misses         32287    32295       +8     
  Partials         404      404              

Files	Coverage Δ
...a/broker/artemis/plugin/security/ServerPlugin.java	0.00% <0.00%> (ø)
...broker/artemis/plugin/security/SecurityPlugin.java	0.00% <0.00%> (ø)
.../artemis/plugin/security/metric/PublishMetric.java	0.00% <0.00%> (ø)

[riccardomodanese]

/request-license-review

[github-actions]

/request-license-review

✔️ All licenses already successfully vetted.

Workflow run (with attached summary files):
https://github.com/eclipse/kapua/actions/runs/8520315310