treewide: add meta.mainProgram (#249601)

pkgs/development/tools/database/sleek/default.nix

···
     homepage = "https://github.com/nrempel/sleek";
     license = licenses.mit;
     maintainers = with maintainers; [ xrelkd ];
+    mainProgram = "sleek";
   };
 }

pkgs/development/tools/rust/sqlx-cli/default.nix

···
     homepage = "https://github.com/launchbadge/sqlx";
     license = licenses.asl20;
     maintainers = with maintainers; [ greizgh xrelkd fd ];
+    mainProgram = "sqlx";
   };
 }

pkgs/tools/admin/eksctl/default.nix

···
-{ lib, buildGoModule, fetchFromGitHub, installShellFiles }:
+{ lib
+, buildGoModule
+, fetchFromGitHub
+, installShellFiles
+}:
 
 buildGoModule rec {
   pname = "eksctl";
···
     homepage = "https://github.com/weaveworks/eksctl";
     license = licenses.asl20;
     maintainers = with maintainers; [ xrelkd Chili-Man ];
+    mainProgram = "eksctl";
   };
 }

pkgs/tools/misc/wit-bindgen/default.nix

···
     homepage = "https://github.com/bytecodealliance/wit-bindgen";
     license = licenses.asl20;
     maintainers = with maintainers; [ xrelkd ];
+    mainProgram = "wit-bindgen";
   };
 }