[BUGFIX] ext:adodb Restrict connection wizard to admins

In the unlikely case ext:datasources is used, there is a potential
information disclosure that content of this table is shown to
non-admin backend users. This is better sanitized with the patch.

Change-Id: I748a0e05b57ac8c6d9c37cdd86fdb093c380dea5
Resolves: #42651
Releases: 6.1, 6.0, 4.7, 4.5
Reviewed-on: https://review.typo3.org/25760
Reviewed-by: Franz G. Jahn
Tested-by: Franz G. Jahn
Reviewed-by: Oliver Klee
Tested-by: Oliver Klee
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn