Adds the ability to have document that wont be synced. This enables
applications to use soledad to store temporary blobs that should be
discarded later instead of unnecessarily keeping the sync loop busy.

-- Resolves: #8819

Sync method to propagate deletions in batch locally.

-- Resolves: #8961

-- Related: #8961

This commit creates a PENDING_DELETE sync status which can be used to
keep track of whats deleted locally in order to propagate to server
later.

-- Related: #8961