Add support for client timezone information

[fmrsabino]

If the user is in a timezone that follows daylight saving, the transaction history grouping is done without taking it into consideration.

Problem

If a user is in a UTC+1 timezone (winter) and UTC+2 (summer), a transaction done during daylight savings will be incorrectly grouped when daylight savings are not observed.

When daylight savings is not being observed, the clients send a UTC+1 difference in milliseconds (3600000 ms). The Safe Client Gateway will then create transaction groups taking only the 3600000 shift into consideration.

If the clients use a solution that takes daylight savings into consideration, this might cause some transactions to be rendered with UTC+2 and potentially making the group that was created with UTC+1 to contain transactions of the following/previous day.

Example

• TX1 done on Sun Jul 30 2023 22:46:47 UTC+0000.
• TX2 done on Sun Jul 30 2023 21:46:47 UTC+0000
• Client on UTC+1 Winter, UTC+2 Summer
• Client is on Winter timezone

1. Client sends timezone offset of +1 hour
2. CGW computes groups with 1 hour difference.
3. CGW returns a group with July 30 (22:46:47 UTC+0000) with transactions TX1 and TX2
4. Clients, aware of daylight savings, shift the header label to July 31 (00:46:47 UTC+2) that will include TX1 and TX2 while there should be two groups rendered: July 31 with TX1 and July 30 with TX2.

The transaction was therefore shifted to a different day on the client side while it should've been grouped correctly on the CGW side.

Expected Result

Given the same example as the one above:

1. Client sends timezone offset of +1 hour
2. CGW computes groups with 1 hour difference and takes into consideration daylight savings.
3. CGW returns two groups:

• July 30 (22:46:47 UTC+0000) with TX1
• July 30 (21:46:47 UTC+0000) with TX2

5. Clients, aware of daylight savings, shift the first header label to July 31 (00:46:47 UTC+2) which includes TX1.