feat: add healthcheck handler & register it as endpoint

[MikaelVallenet]

close gnolang/gno#2650

I've taken the initiative of integrating the addition of the healthcheck feature directly into the faucet pkg, with an option to enable/disable it (enabled by default), because I think it can avoid having to develop this common feature on several projects.

Also, the faucet currently creates a new HTTP router, so to add it externally you'd have to export the router or add an option to set the faucet router when it's created (requiring you to modify both the faucet pkg and the overlay in the gno main repository).

The endpoint can be ping like this:

curl --location --request GET 'http://localhost:8545/health'

[zivkovicmilos]

Thank you for the contribution 🙏

Looks good, the only thing that needs to be changed is making the health endpoint optional -- it should always be on. Please remove related optional functionality for it, and check the linter 🙏

[zivkovicmilos]

Thank you for the quick fix 🙏