feat!: expose pubsub topic in IDecodedMessage

[fryorcraken]

Needed for deterministic message hash.

Ref: #1208

[github-actions]

size-limit report 📦

Path	Size	Loading time (3g)	Running time (snapdragon)	Total time
Waku core	114.56 KB (+0.02% 🔺)	2.3 s (+0.02% 🔺)	644 ms (-22.91% 🔽)	3 s
Waku default setup	366.54 KB (+0.02% 🔺)	7.4 s (+0.02% 🔺)	1.3 s (-12.11% 🔽)	8.6 s
ECIES encryption	27.75 KB (+0.04% 🔺)	556 ms (+0.04% 🔺)	419 ms (+17.9% 🔺)	974 ms
Symmetric encryption	27.76 KB (+0.04% 🔺)	556 ms (+0.04% 🔺)	422 ms (+32.3% 🔺)	977 ms
DNS discovery	108.05 KB (0%)	2.2 s (0%)	615 ms (-6.11% 🔽)	2.8 s
Privacy preserving protocols	114.06 KB (+0.02% 🔺)	2.3 s (+0.02% 🔺)	468 ms (-2.67% 🔽)	2.8 s
Light protocols	115.87 KB (+0.02% 🔺)	2.4 s (+0.02% 🔺)	374 ms (-33.03% 🔽)	2.7 s
History retrieval protocols	115.89 KB (+0.02% 🔺)	2.4 s (+0.02% 🔺)	514 ms (-13.94% 🔽)	2.9 s