fix: hue install failed when postgresql group missing

[giem-git]

Additional comments

Hue configuration fails when postgreql group is absent from ansible inventory.
This is due to a reference to groups['postgresql'] in hue.ini.j2

Fixed by adding a default filter. Besides, we configure a sqlite3 engine by default.

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[giem-git]

Just pushed a simple version.
Without an ansible postgresql group, hue database config will have to be overriden by a tdp_vars_override.