feat: add do command to change MySQL charset to utf8mb4

[Danyal-Faheem]

Additional PR to close #938.

The first part of this work can be found in #1084.

Introduces a new do command convert_mysql_utf8mb4_charset that converts the default and current character and collation of the tables to utf8mb4.

The command has the following options:

• database: the database in which the tables are to be converted. Default: {{ OPENEDX_MYSQL_DATABSE }}
• include: comma separated list of tables on which the upgrade process is to be applied
• exclude: comma separated list of tables to exclude from the upgrade process

The command will perform the following upgrades: - Upgrade all utf8mb3 charset to utf8mb4 - Upgrade collation utf8mb3_general_ci to utf8mb4_unicode_ci - Upgrade collation utf8mb3_bin to utf8mb4_bin - Upgrade collation utf8mb3_* to utf8mb4_*