Add support for multiple flag values via repeated flags using ellipsis syntax - #6198

---

This section details on the original issue you should resolve

<issue_title>wp theme list show multiple status</issue_title>
<issue_description>I am creating an audit script and noticed that you cannot use more than one status with the wp theme list command.

Here is an example on a live site:

wp theme list

Output

+----------------+--------+--------+---------+
| name           | status | update | version |
+----------------+--------+--------+---------+
| woodmart-child | active | none   | 1.0.0   |
| woodmart       | parent | none   | 4.4.0   |
+----------------+--------+--------+---------+

I can filter by one status

wp theme list --status=active

Output

+----------------+--------+--------+---------+
| name           | status | update | version |
+----------------+--------+--------+---------+
| woodmart-child | active | none   | 1.0.0   |
+----------------+--------+--------+---------+

But if I try to get both the active and parent status in one command it fails

wp theme list --status=active,parent

Output

+------+--------+--------+---------+
| name | status | update | version |
+------+--------+--------+---------+
+------+--------+--------+---------+

</issue_description>

<agent_instructions>Similar to the senstive: true annotation, there could be one called multiple: true. Then, when parsing arguments, if doing something like --flag=foo --flag=bar, if multiple: true is set, $assoc_args['flag'] would be an array [ 'foo', 'bar' ]</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@swissspidy Sounds like it might be looking for a status called `active,parent` and not actually doing any splitting to filter by both.

So this would be more of an enhancement. I'd be open to accept a PR that covers all relevant commands and also clearly documents the behavior. Would also be good to check other commands as well to ensure they all behave similarly.</comment_new>
<comment_new>@thelovekesh
@swissspidy IMO It's hard to guess whether the user wants to pass comma-separated strings as multiple strings or the string itself contains the comma. In this case, we can explore the strategy to pass a flag multiple times in case multiple values are intended for a flag.

Example:

$ wp --flag=option1 --flag=option2
# It will be parsed by CLI as `$flag = [ 'option1', 'option2' ]`

$ wp --flag=option1,option2
# It will be parsed by CLI as `$flag = [ 'option1,option2' ]`
```</body></comment_new>
<comment_new><author>@danielbachhuber</author><body>
Related https://github.com/wp-cli/extension-command/issues/159</body></comment_new>
</comments>