Add utf8mb4 client collation to my.cnf in containers

[rfay]

The Problem/Issue/Bug:

mysql import-db and mysql are affected by client config which lacks utf8mb4 (defaults to latin1).

How this PR Solves The Problem:

Add client config to set connection to utf8mb4

Manual Testing Instructions:

Example is coming from @RobertLang, who ran into trouble with imported dbs because of this.

Automated Testing Overview:

We need to add a test to the mysql container to make sure that everything works properly, should be easy enough.

Related Issue Link(s):

Release/Deployment notes:

[RobertLang]

Please check this very basic project:
dbtest.zip

Steps to reproduce the problem with MySQL 5.7 on macOS Catalina 10.15.1:

ddev start
ddev import-db --src=correct_import.sql
=> check phpMyAdmin

(result looks good)

ddev import-db --src=error_import.sql
=> check phpMyAdmin

(result is scrambled)

When the sql file doesn't contain the line /*!40101 SET NAMES utf8mb4 */; the import is done using the default connection encoding which is latin1 for the ddev database container.

When checking the db variables with ddev mysql you see that the default character set for client and connection is latin1.

mysql> show variables like "%character%";
+--------------------------+----------------------------+
| Variable_name            | Value                      |
+--------------------------+----------------------------+
| character_set_client     | latin1                     |
| character_set_connection | latin1                     |
| character_set_database   | utf8mb4                    |
| character_set_filesystem | binary                     |
| character_set_results    | latin1                     |
| character_set_server     | utf8mb4                    |
| character_set_system     | utf8                       |
| character_sets_dir       | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+

I would suggest to make the default connection encoding fit with the default database encoding (which is utf8mb4) to fix this issue.

[rfay]

Thanks for the excellent test. It broke for me with both imports, but with dbimage: drud/ddev-dbserver-mysql-5.7:20191217_utf8mb4_connection (from this PR) in .ddev/config.yaml, it worked fine for me. I'd love it if you'd confirm that behavior, but I think this does it.

I was just using ddev mysql and

mysql> select * from test_table;
+----+---------------------------------------+
| id | testfield                             |
+----+---------------------------------------+
|  1 | Some german umlauts: äöü ß ÄÖÜ        |
|  2 | Some czech text:  Přímé doručení      |
+----+---------------------------------------+
2 rows in set (0.00 sec)