[PIE-1709] Implement Prometheus metric counter for skipped expired transaction messages.

[AbdelStark]

PR description

Follow up PR of #1604
We want to provide Prometheus metrics when the TransactionsMessageProcessor skips some expired messages.

• a prometheus counter is created for skipped messages
• the counter is updated when a message is skipped.
• a log is provided every time a step is hit (default is 1000).

Fixed Issue(s)

#PIE-1709

[NicolasMassart]

Why counting in Pantheon and not just sending an event on the metrics API (received usually by Prometheus in our case) and let Prometheus count and build the aggregated data? It would remove the need to maintain a counter in Pantheon.

[AbdelStark]

Why counting in Pantheon and not just sending an event on the metrics API (received usually by Prometheus in our case) and let Prometheus count and build the aggregated data? It would remove the need to maintain a counter in Pantheon.

The interface actually use Prometheus API.

[NicolasMassart]

Thanks for the change and clarifying the code, LGTM now