Include agenix module and package directly

Avoids adding an extra flake input only to fetch a single module and
package.

Reviewed-by: Aleix Boné <abonerib@bsc.es>
Tested-by: Rodrigo Arias Mallo <rodrigo.arias@bsc.es>

pkgs/agenix/example/passwordfile-user1.age

@@ -0,0 +1,9 @@
+age-encryption.org/v1
+-> ssh-ed25519 KLPP8w s1DYZRlZuSsyhmZCF1lFB+E9vB8bZ/+ZhBRlx8nprwE
+nmYVCsVBrX2CFXXPU+D+bbkkIe/foofp+xoUrg9DHZw
+-> ssh-ed25519 V3XmEA Pwv3oCwcY0DX8rY48UNfsj9RumWsn4dbgorYHCwObgI
+FKxRYkL3JHtJxUwymWDF0rAtJ33BivDI6IfPsfumM90
+-> V'v(/u$-grease em/Vgf 2qDuk
+7I3iiQLPGi1COML9u/JeYkr7EqbSLoU
+--- 57WJRigUGtmcObrssS3s4PvmR8wgh1AOC/ijJn1s3xI
+<EFBFBD>'K<>ƷY&<26>7G<37>O<EFBFBD><4F>Fj
<13>k<EFBFBD>X<EFBFBD><58>BnuJ<75><4A>:9<>(<><7F><EFBFBD>X<EFBFBD>#<23>A<EFBFBD><41><EFBFBD><EFBFBD>ڧj<DAA7>,<02>_<17><><EFBFBD>?<3F>Z<EFBFBD><17>v<EFBFBD><76>V<EFBFBD>96]oks~%<25>c	<04>e^C<>%JQ5<51><H<>z}<7D>C<EFBFBD>,<2C>p<EFBFBD><70>*!W<><57><EFBFBD>A<EFBFBD><41><EFBFBD>҅dC<15>K)<10><>-<2D>y