MySqlHook add support for init_command

[alexbegg]

Description

There is currently no way to pass an init_command connection argument for a mysql connection when using either the mysqlclient or mysql-connector-python libraries with the MySql provider's MySqlHook.

Documentation for connection arguments for mysqlclient library, listing init_command:
https://mysqlclient.readthedocs.io/user_guide.html?highlight=init_command#functions-and-attributes

Documentation for connection arguments for mysql-connector-python library, listing init_command:
https://dev.mysql.com/doc/connector-python/en/connector-python-connectargs.html

There can be many uses for init_command, but also what comes to mind is why do we explicitly provide support to certain connection arguments and not others?

Use case/motivation

For my own use right now I am currently am subclassing the hook and then altering the connection arguments to pass in init_command to set the time_zone session variable to UTC at connection time, like so:

conn_config['init_command'] = r"""SET time_zone = '+00:00';"""

Note: This is just an example, there can be many other uses for init_command besides the example above. Also, I am aware there is a time_zone argument for connections via the mysql-connector-python library, however that argument is not supported by connections made with mysqlclient library. Both libraries do support the init_command argument.

Related issues

No response

Are you willing to submit a PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct

[alexbegg]

I am working on a PR for this, I just need to make sure the tests pass and if a test DAG covering my example use case works.