Allow mysql_config_include_files to contain raw content

[Frazew]

Summary

In some cases, specifying a known src path in mysql_config_include_files is not possible / complicated and it may be much cleaner to provide raw file content to be sent. In that case, we need to use the ansible.builtin.copy module. We can extend the current implementation by simply filtering on whether src or content is set in each item in mysql_config_include_files

This PR also adds a label definition to the loop, that becomes necessary to avoid printing entire files with the default loop label

Example

For example if you want to use mysql_config_include_files with a file stored inside another role (because that's where it's the most practical place to store it currently), you need to:

mysql_config_include_files:
  - { src: "{{ role_path }}/../myrole/files/mysql/myconfig.cnf", force: yes }

Instead, for very simple configuration snippets it's cleaner to store them in the inventory / group_vars, and this PR then allows you to do that:

mysql_config_include_files:
  - dst: myconfig.cnf
    content: |
      [mysqld]
      # ...