Create chore to convert roles to former roles

[pulsejet]

Note: to be done only after #380 and #382 fixed.

• Add a new boolean field permanent to BodyRole which will imply that the role does not expire.
• Ask a human challenge before running the chore along with a confirmation
• Convert each role that a UserProfile has to a former role. Note that roles may be multiple.
• Set the year field from Add year to former role through field #380 to prompted input. Add explicit instructions that the format must be 2018-19 etc.
• Do not convert the roles to former (simply remove) if not official_post (Add flag official_post to BodyRole #382)

[pulsejet]

Implemented as reset-all-roles chore