[network] Implement a smart cache size

[nirvn]

Description

This PR improves QGIS' handling of its network disk cache by using a smart cache size logic that dynamically sizes based on the disk cache storage's available space. The logic is taken from Firefox (https://github.com/mozilla/gecko-dev/blob/e0a62f1391f7d58fab20418adc9310b23708a792/netwerk/cache2/CacheFileIOManager.cpp#L4307), and will results in most users getting a larger cache size.

The objective here is to insure that our default cache size insures we are as friendly as we can to servers hosting XYZ tiles, incl. but not limited to OpenStreetMap.

Users can disable the smart cache size logic in favor of a static cache size in the Options dialog. On that front, the spin box represents MBs instead of KiBs, because we're in 2024 :)

[github-actions]

🪟 Windows builds ready!

Windows builds of this PR are available for testing here. Debug symbols for this build are available here.

(Built from commit f0085c6)

[nirvn]

@rouault , @nyalldawson , @DelazJ , thanks for the reviews, points have been addressed.

[DelazJ]

Thanks @nirvn Looks fine regarding my requests.

[qgis-bot]

@nirvn

This pull request has been tagged for the changelog.

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[qgis-bot]

@nirvn
This pull request has been tagged as requiring documentation.

A documentation ticket will be opened at https://github.com/qgis/QGIS-Documentation when this PR is merged.

Please update the description (not the comments) with helpful description and screenshot to help the work from documentors.
Also, any commit having [needs-doc] or [Needs Documentation] in will see its message pushed to the issue, so please be as verbose as you can.

Thank you!

[qgis-bot]

@nirvn
A documentation ticket has been opened at qgis/QGIS-Documentation#9228
It is your responsibility to visit this ticket and add as much detail as possible for the documentation team to correctly document this change.
Thank you!