Collect metrics from the gateway

[zkokelj]

Why this change is needed

We would like to have some metrics of the gateway usage. We were able to get some of those metrics from the unencrypted database before. But with encrypted database we don't have that ability anymore.

What changes were made as part of this PR

• new metrics package that allows us to count number of users, accounts registered and active users in last month
• we are displaying those statistics every day in logs where we can easily see them

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