Custom local queries

[sosedoff]

This is a tracking issue for the new feature: Custom Local Queries

Background: Pgweb is a basic database browser and query runner, and does not have a way of executing any pre-defined user queries stored locally. There's no persistent level (aside from the filesystem) for storing these queries. When developing locally, or against a remote database, having an easy and quick access to a set of database-specific queries (mostly for troubleshooting or fast data selection) would be very convenient and helpful. We could allow Pgweb to read sql files (query+metadata?) from ~/.pgweb/queries/... and expose them in a separate Queries UI tab. This behavior smells like a BI use-case, but it's not.

Ideas:

• Store queries locally at ~/.pgweb/queries/ directory.
• Allow queries to be available in different databases (local or remote) identified by name. We could encode database match pattern (among other things) in the query file via sql comment: -- pgweb:"OPTIONS". Any file that does not have a comment should be ignored.
• Should be able to set max execution time

Here's an example query file with pgweb metadata:

-- pgweb: database=myapp                 <- only available in "myappdb", remotely or locally
-- pgweb: database=myapp; host=localhost <- only available in "myappdb" locally
-- pgweb: database=myapp_*;              <- matching any database starting with "myapp", e.g. "myapp_development, "myapp_test"
-- pgweb: database=*;                    <- available for all connections and databases
-- pgweb: database=*;user=admin          <- available only for "admin" users on any connection

SELECT * FROM orders 
WHERE status = 'pending' AND amount > 1000 
ORDER BY submitted_at DESC 
LIMIT 100