Helpscout - Allow users to accept invites

[caleballdrin]

Description

https://secure.helpscout.net/conversation/2731091026/1241412?folderId=7669074

• Accept account invites
• Redirect old links

Checklist:

• I have given my PR a title with the format "MPDX-(JIRA#) (summary sentence max 80 chars)"
• I have applied the appropriate labels. (Add the label "On Staging" to get the branch automatically merged into staging.)
• I have requested a review from another person on the project

[github-actions]

Bundle sizes [mpdx-react]

Compared against e1c3140

Route	Size (gzipped)	Diff
/acceptInvite	83.08 KB	added
/account_lists/[accountListId]/accept_invite/[inviteId]	80.16 KB	added
/organizations/[orgId]/accept_invite/[inviteId]	80.16 KB	added

[dr-bizz]

Looking great! I left a few comments, but that is it. Great work. I don't want to block you so I will approve this.

[canac]

Great work! I think the most important thing from my comments is removing useAccountListId() because unless I'm mistaken it will either always return undefined or might even be returning the inviter's account list id. It might be working because of the default account list redirect logic you implemented. But if we're relying on that, let's make it explicit and redirect the user to /accountLists/_/settings/preferences (with an underscore as an intentionally invalid account list id or some other clearly invalid id) and add a code comment to document what we're doing.

[canac]

Also, old organization invite links don't redirect to the new URLs but that might be OK because they might not be as common.