Add/boost/cache-preloading-cornerstone-pages

[LiamSarsfield]

Fixes #

Proposed changes:

Other information:

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Testing instructions:

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/plugins/boost/app/modules/optimizations/page-cache/Page_Cache.php	0/53 (0.00%)	0.00%	3 ❤️‍🩹

1 file is newly checked for coverage.

File	Coverage
projects/plugins/boost/app/modules/optimizations/page-cache/Cache_Preload.php	0/33 (0.00%) 💔

Full summary · PHP report · JS report

_{Add label I don't care about code coverage for this PR Use this label to ignore the check for insufficient code coveage. to override the failing coverage check.}