Introduction of local services authentication added a configuration file
containing the auth tokens for each service. There were different names
for that file, and this commit standardizes all of them to the same
value: /etc/soledad/services.tokens

Soledad Server was previously using something in /srv to store blobs in
the server side. Debian/lintian doesn't like that at all, so we are
changing to /var/lib/soledad/blobs.

Closes: #8948

From code review.

-- Related: #8945

This commit makes all write calls happen inside the same thread that
opened the blob handle. Doing it outside using FileBodyProducer will
yield and run the writes across random reactor threads. This is an
attempt to fix #8945

-- Resolves: #8945

Moved schema creation and migrations to the pragma locked call, so we
avoid it running concurrently on a thread pool.

-- Resolves: #8945

It isn't closed by Twisted like the producer is.

-- Resolves: #8924
-- Related: #8932

Adds two new columns for sync status and retries. Also some initial
rough logic for upload retry limiting.

-- Resolves: #8823
-- Related: #8822