feat(web/blog): add ability to specify post author

Anyone is free to pen a post for tvl.fyi if they want, so being able
to attribute the author might be useful.

This wasn't originally a feature because I wrote //web/blog only for
tazj.in initially.

Change-Id: Ibc50b53f92113a82a53ce40bb5defa18e926cc10
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6560
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
Reviewed-by: grfn <grfn@gws.fyi>

web/tvl/blog/default.nix

@@ -13,6 +13,7 @@
       title = "Tvix: We are rewriting Nix";
       date = 1638381387;
       content = ./rewriting-nix.md;
+      author = "tazjin";
     }
 
     {
@@ -20,6 +21,7 @@
       title = "Tvix Status - September '22";
       date = 1662995534;
       content = ./tvix-status-202209.md;
+      author = "tazjin";
       draft = true;
     }
   ];