Request: pickup deadline should be calculated starting from the checkin date

[ManaDeweerdt]

Describe the bug

For now, the pickup deadline is calculated starting from the request date.
Ex : https://ils.bib.uclouvain.be/professional/records/items/detail/3259079
https://ils.bib.uclouvain.be/professional/records/items/detail/3511120
https://ils.bib.uclouvain.be/professional/records/items/detail/3499505

It appears that when a request is validated with 'validate_first_pending' the request transaction_date isn't updated. It's important to do that because the loan request_expiration_date is calculated on this date.

To Reproduce

1. Place a request on a borrowed item. (or find a borrowed item with a request on it).
2. Wait one day and checkin the item.
3. See the pickup deadline.

Expected behavior

The pickup deadline should be calculated from the checkin date.

Context

• server: ucl instance
• version: v1.8.0 or the commit hash (see frontpage).
• browser: [if relevant, e.g. chrome, safari, version 78].

Screenshots

The 'validate request' date should be the same as the checkin date. In this example, it displays the same date as the request date.

Other example

Additional context