Add deprecation warning for SQLite

Mortimer Pavlitskirequested to merge
mortimer/deprecate-sqlite into master

SQLite is being deprecated for buildgird, Add deprecation warning and instructions for upgrade.

NB: the link currently points to an old compose file but will be correct once buildgrid.hub.docker.com!26 (merged) is merged.

Edited by Mortimer Pavlitski

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