Speed up bootstrap by preloading manifests for base platforms

[bdraco]

Will conflict with #110136 This one should merge first

With the combination of the two my large installs are now initializing in ~14-16s consistently

Proposed change

Speed up bootstrap by preloading manifests for base platforms

#107312 did a lot to reduce executor jobs at startup, but we still ended up with a single job per base platform. By loading them earlier we reduce lock contention and executor jobs.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

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• This PR fixes or closes issue: fixes #
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[emontnemery]

LGTM, thanks @bdraco 👍

[bdraco]

thanks