Rename filter methods of TodosFinder to indicate they also accept multiple items

Within #31914 (closed) we added support to filter for multiple items with these params:

• :author_id
• :project_id
• :state
• :type
• :group_id

We should rename these params (or add the possibility to also provide their pluralized version (project_ids, group_ids...) to indicate they are also able to handle multiple items.

The following discussion from !19618 (merged) should be addressed:

• @reprazent started a discussion: (+2 comments)

  Will we be changing the param from project_id to project_ids ? Do we need to support both during the transition?