Make "foreign key navigation" bi-directional

Currently Postico can follow a foreign key (open a "foreign key pop-up window") when browsing the table containing the foreign key, but the rverse is not true.
e.g table_a.id references table_b.id
when browsing table_a, an icon is offered to pop-up table_b.
when browsing table_b there is no icon to navigate to table_a.
I suggest adding this.

No files, tests, or entry points are named. Start by tracing the existing foreign-key pop-up navigation while browsing a table, then identify how the schema exposes tables that reference the current table. Done means browsing the referenced table offers a matching navigation icon to each table that points to it.

Written by the indexing model from the issue text.