treewide: add meta.mainProgram

Related PR: NixOS#246386

pkgs/applications/misc/rofi-rbw/default.nix

···
     license = licenses.mit;
     maintainers = with maintainers; [ equirosa dit7ya ];
     platforms = platforms.linux;
+    mainProgram = "rofi-rbw";
   };
 }

pkgs/development/node-packages/main-programs.nix

···
   firebase-tools = "firebase";
   fkill-cli = "fkill";
   fleek-cli = "fleek";
+  flood = "flood";
   git-run = "gr";
   gitmoji-cli = "gitmoji";
   graphql-cli = "graphql";

pkgs/development/tools/continuous-integration/drone-runner-docker/default.nix

···
     license = licenses.unfreeRedistributable;
     homepage = "https://github.com/drone-runners/drone-runner-docker";
     description = "Drone pipeline runner that executes builds inside Docker containers";
+    mainProgram = "drone-runner-docker";
   };
 }

pkgs/development/tools/continuous-integration/drone-runner-exec/default.nix

···
     # https://polyformproject.org/licenses/small-business/1.0.0/
     license = licenses.unfree;
     maintainers = with maintainers; [ mic92 ];
+    mainProgram = "drone-runner-exec";
   };
 }

pkgs/development/tools/continuous-integration/drone-runner-ssh/default.nix

···
     homepage = "https://github.com/drone-runners/drone-runner-ssh";
     license = licenses.unfreeRedistributable;
     maintainers = teams.c3d2.members;
+    mainProgram = "drone-runner-ssh";
   };
 }

pkgs/development/tools/continuous-integration/woodpecker/cli.nix

···
 
   meta = common.meta // {
     description = "Command line client for the Woodpecker Continuous Integration server";
+    mainProgram = "woodpecker-cli";
   };
 }

pkgs/games/steam/steam.nix

···
     homepage = "https://store.steampowered.com/";
     license = licenses.unfreeRedistributable;
     maintainers = with maintainers; [ jagajaga jonringer ];
+    mainProgram = "steam";
   };
 }

pkgs/servers/nginx-sso/default.nix

···
     homepage = "https://github.com/Luzifer/nginx-sso";
     license = licenses.asl20;
     maintainers = with maintainers; [ delroth ];
+    mainProgram = "nginx-sso";
   };
 }

pkgs/tools/security/rage/default.nix

···
     changelog = "https://github.com/str4d/rage/raw/v${version}/rage/CHANGELOG.md";
     license = with licenses; [ asl20 mit ]; # either at your option
     maintainers = with maintainers; [ marsam ryantm ];
+    mainProgram = "rage";
   };
 }

pkgs/tools/text/gawk/default.nix

···
     license = licenses.gpl3Plus;
     platforms = platforms.unix ++ platforms.windows;
     maintainers = [ ];
+    mainProgram = "gawk";
   };
 }