fix(web/blog): make base URL configurable for atom feeds

This was previously hardcoded to tazj.in, which is not going to work
of course.

Instead it now takes the blog config which has a new baseUrl
parameter. For ease of use, the configs of my and the TVL blog have
been moved into a location that is accessible in the tree for reuse.

Change-Id: I94e71aaa7859db4380eb7013740a17f6b6a02620
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3777
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>

users/tazjin/blog/default.nix

@@ -5,8 +5,9 @@ with depot.nix.yants;
 let
   inherit (builtins) hasAttr filter;
 
-  blogConfig = {
+  config = {
     name = "tazjin's blog";
+    baseUrl = "https://tazj.in/blog";
 
     footer = ''
       <p class="footer">
@@ -26,12 +27,12 @@ let
     mkdir -p $out
 
     ${lib.concatStringsSep "\n" (map (post:
-      "cp ${renderPost blogConfig post} $out/${post.key}.html"
+      "cp ${renderPost config post} $out/${post.key}.html"
     ) posts)}
   '';
 
 in {
-  inherit posts rendered;
+  inherit posts rendered config;
 
   # Generate embeddable nginx configuration for redirects from old post URLs
   oldRedirects = lib.concatStringsSep "\n" (map (post: ''

users/tazjin/homepage/feed.nix

@@ -22,7 +22,7 @@ let
     };
   });
 
-  allEntries = (map blog.toFeedEntry depot.users.tazjin.blog.posts)
+  allEntries = (with depot.users.tazjin.blog; map (blog.toFeedEntry config) posts)
              ++ (map pageEntryToEntry pageEntries);
 
   feed = {