DB: fix DB connection and query format

[danielbeardsley]

Pulldasher was totally broken and would boot until it ran a REPLACE INTO query and then crash.

oof, see the second change.

First: The .query().then() was just changed to make use of the new
promise interface instead of promisifying the old callback interface.
It wasn't the problem.

Second: Add support for utf8mb3 to the library (we'll open a pull to add
it upstream). See the code comment.

[davidrans]

CR ☕

[danielbeardsley]

This seems to be working fine now!

QA 👍

I've opened a pull upstream: sidorares/node-mysql2#3007

[djmetzle]

Ref: https://github.com/iFixit/server-templates/issues/4731

Are we still using mb3 for the metrics schema?

[davidrans]

The tables and columns are all mb4, but some of the mysql defaults are still mb3:

mysql> SHOW VARIABLES LIKE 'character_set_server';
SHOW VARIABLES LIKE 'collation_server';
+----------------------+---------+
| Variable_name        | Value   |
+----------------------+---------+
| character_set_server | utf8mb3 |
+----------------------+---------+
1 row in set (0.00 sec)

+------------------+--------------------+
| Variable_name    | Value              |
+------------------+--------------------+
| collation_server | utf8mb3_unicode_ci |
+------------------+--------------------+
1 row in set (0.00 sec)