Upgrade PostgreSQL to 15

[leplatrem]

No description provided.

[robhudson]

I looked at this locally. It fails intermittently.

The 500 resp.content is:

{
  "status": "error",
  "checks": {
    "database": "error"
  },
  "details": {
    "database": {
      "status": "error",
      "level": 40,
      "messages": {
        "db.0002": "Contacts table empty"
      }
    }
  }
}

The health check is counting the number of contacts and getting a -1 which doesn't pass the this assertion, so the test fails.

There's a comment for the count_total_contacts function:

    Since the table is huge, we rely on the PostgreSQL internal
    catalog to retrieve an approximate size efficiently.
    This metadata is refreshed on `VACUUM` or `ANALYSIS` which
    is run regularly by default on our database instances.

Perhaps something changed slightly with those between Postgresql 12 and 15?

[robhudson]

Updated with a fallback for cases where the table has not yet been vacuumed or analyzed. In production this fallback will likely never run, but for unit tests it prevents the previous error. Another option is to force analyze the table in the tests but the code here seemed like a safe and straight-forward option.