Snapshots contain incorrect config items

Problem/Motivation

After the refactoring introduced in #2981701: Config snapshot incorrect after config db pull, when multiple extensions are snapshotted consecutively, the resulting snapshots contain the cumulative configuration provided by all extensions, rather than that of only the extension being processed.

Proposed resolution

Need to clear out configuration provider storage prior to making new snapshot.

Remaining tasks

User interface changes

API changes

Data model changes