feat: adding metrics to provide insights about the module

[jaybxyz]

Description

closes: #59

Tasks

• Add helpful metrics to provide insights about the module

Output

# HELP budget budget
# TYPE budget gauge
budget{collection_address="cosmos1xxx",denom="stake"} 185

---

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[jaybxyz]

TestInitGenesis fails due to index out of range error. Let me go check and resolve it.

[jaybxyz]

budgetsBySource.CollectionCoins[i] triggers the index out of range error because defer func() delays the execution of the function until the nearby functions return. Since the deferred func sees the recent value of i, we should add the following code inside the for loop.

i := i
collectionCoins := budgetsBySource.CollectionCoins

[dongsam]

LGTM