Add watchlisting options for autowelcome

[g1ftzwerg]

This is not a pressing issue by any means, but with autowelcoming incoming, it would be nice to have a feature that overrides the enwiki autowatchlisting preferences and allows users to have the option of selecting whether they want to (temporarily or indefinitely) watchlist the talk pages of accounts they created.

[dqwiki]

Global preferences would have to be taken into account also if we take this on.
That said, I'm not sure the current implementation plan for auto-welcoming, and how it's authenticated/if watchlist changes are even authorized (we have to get special permission to do more than just identify the user)

[stwalkerster]

Global preferences are somewhat meaningless here; at the moment we default to the user's on-wiki preferences for editing a page, by virtue of not telling MediaWiki what to do with the watchlist. MediaWiki decides whether or not to add the page to the user's watchlist.

We can override this on a per-edit basis (in other words, whenever we do an auto-welcome) really easily, by just adding the relevant parameters to the page edit request, specifically ?action=edit&watchlist=watch or ?action=edit&watchlist=nochange. We can even set the expiry as needed with the watchlistexpiry parameter.

[stwalkerster]

Specifically, where we'd need to modify the edit request is here, though my expectation would be to look up the preferences and pass parameters in from here rather than look up user preferences in the helper class.

[ElHefWiki]

Support this - I don't have WP set up to watchlist every edit, but rather have Twinkle set to temporarily watchlist anyone I welcome. It would be nice (though certainly not critical) to be able to set up ACC to do the same.

[stwalkerster]

No longer needs schema changes following preferences refactor

[stwalkerster]

If someone else wants to pick this up, #566 has guidance on adding new preferences. With the guidance for where and what to change to set the watchlist preferences in the comment above, this should be doable by someone other than me. 😀

I'd suggest a dropdown in preferences for possible options ranging from "Use on-wiki preference", "Don't watchlist", "Watchlist permanently", and a reasonable range of "Watchlist for X time" options.