feat: allow setting the base denom

[emidev98]

Description

Allow changing the default base denom from types with any other previously registered denom.

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[julienrbrt]

code-wise lgtm, but I am curious about the use-case of this.
When do you need to change the base denom?

[emidev98]

Imagine if you want to register multiple coin denoms to operate with different precision on different applications (while coding for a core module or on cosmwasm smart contract) but you don't want to change the default denom on the unit with more precision (as coded here).

E.g.: when upgrading the core for backwards compatibility, register multiple denoms with precision 10^-3, 10^-6, 10^-9 but use the same old denom with 10^-6 precision.