TeX can not natively query the contents of a directory. So from within TeX you can't get a list of .bib files in a directory and loop over them unless you involve shell escape or LuaTeX.
With shell escape you can run ls or similar on the directory and then parse the returned list, with LuaTeX you can use Lua to access the file system, see How to iterate through the name of files in a folder. You could then loop over that list and apply \addbibresource for each item.
Biber could possibly query the contents of folders, but it has no user-facing interface to allow you to do that at the moment.
I would assume that the number of .bib files and their names are fairly stable, so you could compile a list of these files with \addbibresource around each and \input that list in all of your documents.
\addbibresource: "Also note that the\bibliographywhich accepts as argument a comma separeted list of bib files. But it seems to me, there is no escape from listing the individual files, so not much is gained by this in the end.