feat: add Proof.type field

[raphodn]

What

New field Proof.type to be able to differentiate proofs.
This field is validated by an enum that defines a list of possible values : PRICE_TAG, RECEIPT, GDPR_REQUEST, RETAILER

[raphael0202]

What kind of proof retailers would submit? Isn't it enough that the data comes from a "verified" account (i.e account with an email address from the retailer)?

[raphodn]

fyi I was including the COOPs in the RETAILER type

• it could be just a screenshot of their CMS with a date ?
• if we decide to add a price filter on "has proof" or not, it would be better to ask retailers to send a proof, no ?
• or indeed like you say, we have a list of "verified" accounts, and we consider it a proxy to a proof

[raphael0202]

On Open Food Facts pro platform, we assume the data coming from trusted source to be accurate, as they're the source of the data it makes sense not to ask for an additional proof in my opinion.

if we decide to add a price filter on "has proof" or not, it would be better to ask retailers to send a proof, no ?

I was considering to add a flag "is_retailer" to the user table, so that we know which prices come from a verified source.

[raphodn]

ok i removed it !