feat(gnokey): add querying realm balances

[leohhhn]

Description

Closes: #2469

This PR adds code to the handler in gnokey that extends the bank/balances functionality to allow users to fetch the balance of a realm given its pkgpath, ie bank/balances/gno.land/r/demo/wugnot.

Initially I wanted to implement this functionality in the handler for tm2/sdk/bank, but in order to not introduce more tm2<>gno dependencies, I did it in the gnokey query handler. Then, I realized that that handler is also under tm2, in tm2/pkg/crypto/keys/client/query.go :/

Contributors' checklist...

• [x] Added new tests, or not needed, or not feasible
• [x] Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• [x] Updated the official documentation or not needed
• [x] No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• [x] Added references to related issues and PRs
• [x] Provided any useful hints for running manual tests
• [x] Added new benchmarks to generated graphs, if any. More info here.