nix: fix nix run by setting mainProgram to waku

[jakubgs]

Otherwise it fails with:

 > nix run github:status-im/go-waku
error: unable to execute '/nix/store/xsmhw1yqz5w9bdgfsprxmhcycl7011wz-go-waku/bin/go-waku': No such file or directory

 > ls -l /nix/store/xsmhw1yqz5w9bdgfsprxmhcycl7011wz-go-waku/bin
total 37914
-r-xr-xr-x 1 root root 38775544 Jan  1  1970 waku

The other option is to change the output binary path from waku to go-waku, but that would have to be done by either renaming cmd/waku to cmd/go-waku or some awkward patching of buildGo119Module.

[status-im-auto]

Jenkins Builds

❔	Commit	#️⃣	Finished (UTC)	Duration	Platform	Result
✔️	38de493	#1	2023-03-06 13:44:57	~1 min	linux	📦deb
✔️	38de493	#1	2023-03-06 13:45:44	~1 min	nix-flake	📄log
✔️	38de493	#1	2023-03-06 13:47:25	~3 min	android	📦tgz
✔️	38de493	#1	2023-03-06 13:47:37	~3 min	ios	📦tgz

[jakubgs]

Appears to be working:

 > nix run 'github:status-im/go-waku?ref=nix/fix-nix-run' 
2023-03-06T14:49:21.121+0100	INFO	gowaku	waku/node.go:238	Version details 	{"node": "16Uiu2HAmNKjWkyB5DA1gRwrDEjNAkTt2tsQBg7tmMghZfnbgdZMy", "version": "0.5.1", "commit": "38de493"}
2023-03-06T14:49:21.121+0100	INFO	gowaku.node2.timesource	timesource/ntp.go:169	starting service	{"node": "16Uiu2HAmNKjWkyB5DA1gRwrDEjNAkTt2tsQBg7tmMghZfnbgdZMy"}
2023-03-06T14:49:21.121+0100	INFO	gowaku.node2	node/keepalive.go:34	setting up ping protocol	{"node": "16Uiu2HAmNKjWkyB5DA1gRwrDEjNAkTt2tsQBg7tmMghZfnbgdZMy", "duration": 300}
2023-03-06T14:49:21.121+0100	INFO	gowaku.node2	node/wakunode2.go:264	listening	{"node": "16Uiu2HAmNKjWkyB5DA1gRwrDEjNAkTt2tsQBg7tmMghZfnbgdZMy", "multiaddr": ["/ip4/192.168.1.101/tcp/60000/p2p/16Uiu2HAmNKjWkyB5DA1gRwrDEjNAkTt2tsQBg7tmMghZfnbgdZMy", "/ip4/127.0.0.1/tcp/60000/p2p/16Uiu2HAmNKjWkyB5DA1gRwrDEjNAkTt2tsQBg7tmMghZfnbgdZMy"]}