[WPB-8707] Remove phone functionality in the development client API version

[mdimjasevic]

The PR removes phone numbers and phone functionality from the development client API version, namely from v6.

A couple of up-for-debate choices have been made, and I'm open to discuss them:

1. The phone key was dropped from Brig's team_invitation DB table. Previous releases were still reading this column. As there is no Team Settings UI action to enter a phone number, so the column was never written to; hence not reading from the column will not miss to read actual phone numbers. Therefore, during deployment this will lead to benign 5xx errors. Related to this, the "phone" field for endpoints that get one or more team invitations is silently ignored and the field has been removed from the request body of the v6 endpoint to send a team invitation.
2. The "phone" field of the request body to POST /register is now ignored instead of giving an error.

Tracked by https://wearezeta.atlassian.net/browse/WPB-8707.

Checklist

• Remove the POST /login/send endpoint,
• Remove the PUT /self/phone endpoint,
• Remove the DELETE /self/phone endpoint,
• Modify the GET /self endpoint to remove the phone key from the response,
• Modify the GET /activate endpoint to remove the phone key from the response,
• Modify the POST /activate/send endpoint to remove the phone key from the request body, i.e., no ability to send an activation code via SMS,
• Drop the phone field in the response to the GET /teams/invitations/info endpoint,
• Drop the phone field in the response to the GET /teams/{tid}/invitations endpoint,
• Drop the phone field in the response to the GET /teams/{tid}/invitations/{iid} endpoint,
• Drop the phone field from the request body of POST /teams/{tid}/invitations endpoint,
• Modify the POST /register endpoint to remove the phone key both from the request and the response,
• Modify the POST /login endpoint by removing phone-related keys, namely phone and code, from the request body,
• Modify the POST /activate endpoint by removing the phone key from the request body,
• Add a new entry in an appropriate subdirectory of changelog.d
• Read and follow the PR guidelines

[battermann]

Looks good. If there is a good reason not to use the VersionedReqBody wrapper, I'd like to know, and then it's good to go. Otherwise, it might be a sensible change?

[battermann]

I think we have a special type that can be used here as a wrapper: VersionedReqBody

[battermann]

Same as above

[battermann]

Same as above... and more below, will not comment on all