sage.databases: Use sage.feature to define database file system location

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... as done in #25825 for `sage.databases.cremona` and in #30607 for `sage.databases.jones`.

This would eliminate direct use of `SAGE_SHARE` (`SAGE_LOCAL`) from `sage.databases`.

CC:  @antonio-rojas @kiwifb @tobiasdiez @videlec

Component: **refactoring**

Keywords: **sd111**

_Issue created by migration from https://trac.sagemath.org/ticket/30819_

