Adding global_synchronized_cache in valhalla_build_config

[AurelienLP]

Issue

#1850

Tasklist

• Add tests
• Review - you must request approval to merge any PR to master
• Add #fixes with the issue number that this PR addresses
• Generally use squash merge to rebase and clean comments before merging
• Update the changelog
• Update relevant documentation

[dnesbitt61]

I might caution that I have been seeing some issues during data generation (valhalla_build_tiles) with some settings when "global_synchronized_cache": true is set in the config. I do not recommend having this set to true during the tile generation process.

[AurelienLP]

Hi @dnesbitt61,

I've been experiencing this for the last couple weeks indeed. I think that trying to fix this will be a lot tougher than just not using it the tile generation process.

Thank you very much for this valuable warning!