Query-exporter

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- Track doomed queries on a per-database basis (16).
- Add ``--version`` option.

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- Support passing sets of parameters for queries.

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- Enable autocommit on connection (10).

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- Support custom labels in metrics, setting values from queries result (7).
- Suport matching metrics by query result column name instead of order.
- Disable queries that will certainly always fail (e.g. because of invalid.
returned column names/number) (6).
- Support disconnecting from after each query (8).
- Rework tests to use actually SQLite in-memory databases instead of fakes.

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- Add a ``queries`` and ``database_errors`` metrics labeled by database (1).
- Support database DSNs defined as ``env:<VARNAME>`` to supply the dns from the
environment (5).

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- Change default port to 9560 (to make it unique).