feat(third_party/gopkgs): add charmbracelet/{bubbletea,bubbles}

A small go TUI framework based on the Elm Architecture.

Change-Id: I0c400a7b25af682735bfc5061db179e5d1dd75ab
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2853
Reviewed-by: Profpatsch <mail@profpatsch.de>
Reviewed-by: lukegb <lukegb@tvl.fyi>
Tested-by: BuildkiteCI

third_party/gopkgs/github.com/muesli/termenv/default.nix

@@ -0,0 +1,19 @@
+{ depot, pkgs, ... }:
+
+depot.nix.buildGo.external {
+  path = "github.com/muesli/termenv";
+  src = pkgs.fetchFromGitHub {
+    owner = "muesli";
+    repo = "termenv";
+    # unreleased version required by bubbletea
+    rev = "v0.8.1";
+    sha256 = "0m24ljq1nq7z933fcvg99fw0fhxj9rb5ll4rlay7z2f2p59mrbdp";
+  };
+
+  deps = with depot.third_party; [
+    gopkgs."github.com".lucasb-eyer.go-colorful
+    gopkgs."github.com".mattn.go-isatty
+    gopkgs."github.com".mattn.go-runewidth
+    gopkgs."golang.org".x.sys.unix
+  ];
+}