feat: get keyring backend (#11484)

## Description

This PR introduces a getter for the keyring backend type used in the keyring config. This is useful to disable endpoints whenever the keyring `test` backend is used. This is a workaround since the SDK keyring dependency doesn't support locking accounts. See 99designs/keyring#85 for context.

Attack on ethereum that affects Ethermint chain validators/nodes using `keyring_backend=test`, making their funds remotely accessible via `eth_sendTransaction`

https://blog.ethereum.org/2015/08/29/security-alert-insecurely-configured-geth-can-make-funds-remotely-accessible/

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(cherry picked from commit 2083bc8)