feat: add Markdown Preview and Obsidian, update startup screen and cleanup lsp config (#8)

Added Markdown Preview and the Obsidian plugins.
Updated the Startup screen with links to Github Copilot and Obsidian
Moved the helm-vim plugin from a seperate file into the lsp.nix file.

config/plugins/utils/obsidian.nix

@@ -0,0 +1,25 @@
+{
+  plugins.obsidian = {
+    enable = true;
+    settings = {
+      workspaces = [
+        {
+          name = "SecondBrain";
+          path = "~/projects/personal/SecondBrain";
+        }
+      ];
+      templates = {
+        subdir = "templates";
+        dateFormat = "%Y-%m-%d";
+        timeFormat = "%H:%M";
+        substitutions = {};
+      };
+
+      dailyNotes = {
+        folder = "0_Daily_Notes";
+        dateFormat = "%Y-%m-%d";
+        aliasFormat = "%B %-d, %Y";
+      };
+    };
+  };
+}