Preload adaptative batch

[MathieuLamiot]

Description

When preparing preload batches, the batch size will be adapted based on the average duration of a request to avoid flooding servers with requests if they take too long.
To get the estimate of the request duration, we do a blocking request from time to time when triggering the preload, and measure the timing.

Fixes #6396

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality).

Is the solution different from the one proposed during the grooming?

Yes, on top of the original idea, we added an average mechanism that keeps track of the average request time through transients.

Checklists

Generic development checklist

• My code follows the style guidelines of this project, with adapted comments and without new warnings.
• I have added unit and integration tests that prove my fix is effective or that my feature works.
• The CI passes locally with my changes (including unit tests, integration tests, linter).
• Any dependent changes have been merged and published in downstream modules.
• If applicable, I have made corresponding changes to the documentation. Provide a link to the documentation.

Test summary

• I triggered all changed lines of code at least once without new errors/warnings/notices.
• I validated all Acceptance Criteria of the related issues. (If applicable, provide proof).
• I validated all test plan the QA Review asked me to.

Tested locally and on the gamma website by checking transients and scheduled actions.

[MathieuLamiot]

@Khadreal Hey, I just pushed a small change to enforce the max batch size after the min batch size. This is for the case there are already 45 actions in the AS queue. In this case, no matter what, we don't want to add more to the AS queue. So the max has to be enforced after.
Checking the tests now