This commit adds overlayDatabaseMode to AugmentationProperties and
creates a placeholder getOverlayDatabaseMode() function, with the
necessary inputs, to populate it.

This commit populates getOverlayDatabaseMode() in config-utils with the
same code from getOverlayDatabaseMode() in init.

This commit changes databaseInitCluster() to use overlayDatabaseMode
from AugmentationProperties instead of the overlayDatabaseMode
parameter. There is no behavior change because both overlayDatabaseMode
values are computed the same way.

The commit then cleans up the overlayDatabaseMode parameter and the code
paths that feed into it.

This commit changes getOverlayDatabaseMode so that, when
Feature.OverlayAnalysis is enabled, it calculates the overlay database
mode automatically based on analysis metadata. If we are analyzing the
default branch, use OverlayBase, and if we are analyzing a PR, use
Overlay.

If CODEQL_OVERLAY_DATABASE_MODE is set to a valid overlay database mode,
that environment variable still takes precedence.

This commit adds useOverlayDatabaseCaching to AugmentationProperties to
indicate whether the action should upload overlay-base databases to the
actions cache and to download a cached overlay-base database when
creating an overlay database.