Add "persistence" types (data, cache, or index) to tables, and tweak what "storage dump" dumps

Summary:
Ref T13000. This marks each table as either "data" (normal data), "cache" (automatically rebuilt, no need to ever dump) or "index" (can be manually rebuilt).

By default, `bin/storage dump` dumps data and index tables, but not cache tables.

With `--no-indexes`, it dumps only data tables. Indexes can be rebuilt after a restore with `bin/search index --all ...`.

Test Plan:
  - Ran `--no-indexes` and normal dumps with `--trace`, verified that cache and index (former case) or cache only (latter case) tables were dumped with `--no-data`.
  - Verified dump has the same number of `CREATE TABLE` statements as before the changes.
  - Reviewed persistence tags in the web UI (note Ferret engine tables are "Index"):

{F5210886}

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13000

Differential Revision: https://secure.phabricator.com/D18682

src/docs/user/configuration/configuring_backups.diviner

@@ -145,6 +145,24 @@ present a risk. If you restrict access to the Phabricator host or database, you
 should also restrict access to the backups.
 
 
+Skipping Indexes
+================
+
+By default, `bin/storage dump` does not dump all of the data in the database:
+it skips some caches which can be rebuilt automatically and do not need to be
+backed up. Some of these caches are very large, so the size of the dump may
+be significantly smaller than the size of the databases.
+
+If you have a large amount of data, you can specify `--no-indexes` when taking
+a database dump to skip additional tables which contain search indexes. This
+will reduce the size (and increase the speed) of the backup. This is an
+advanced option which most installs will not benefit from.
+
+This index data can be rebuilt after a restore, but will not be rebuilt
+automatically. If you choose to use this flag, you must manually rebuild
+indexes after a restore (for details, see ((reindex))).
+
+
 Next Steps
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