Insert all on a collection with the same timestamp

[jyeshe]

Description

This PR changes the inserted_at set when calling Repo.insert_all to have as per requirement the same value for all records.
In order to adhere to the order given by the user on the insert, the pagination and cursor are changed to use a sequence number.

Closes #2711

Validation steps

1. Send a POST to /collections/new-collection-name with a JSON body having the items field.
2. Send a GET to /collections/new-collection-name and check that createdAt are equal and the order of the keys is the same as on the insert.

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Pre-submission checklist

• I have performed a self-review of my code.
• I have implemented and tested all related authorization policies. (e.g., :owner, :admin, :editor, :viewer)
• I have updated the changelog.
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[jyeshe]

Test failed due to unrelated flaky

[jyeshe]

@stuartc thanks for asking, here are the stats for inserting 300 rounds of 2 parallel put_all (2 collections) with 5000 items each put_all:

Average: 516.225ms
Std Deviation: 363.52131213314027ms

database docker (localhost):

docker create --cpus=2.0 --memory=8g --name lightning-postgres --mount source=lightning-postgres-data,target=/var/lib/postgresql/data   --publish 5432:5432   -e POSTGRES_PASSWORD=postgres   postgres:15.3-alpine

disk perf:

$ dd if=/dev/zero of=/tmp/test.img bs=10MB count=100
100+0 records in
100+0 records out
1000000000 bytes (1,0 GB, 954 MiB) copied, 3,26877 s, 306 MB/s

Without the two last indexes (on updated_at and id) not much difference on a standalone, without any other load:

Average: 474.08666666666664ms
Std Deviation: 323.6109894439448ms

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.05%. Comparing base (7fcc9cb) to head (a7824f0).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2712      +/-   ##
==========================================
- Coverage   91.06%   91.05%   -0.01%     
==========================================
  Files         333      333              
  Lines       11708    11708              
==========================================
- Hits        10662    10661       -1     
- Misses       1046     1047       +1     

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