Add PathEscape to MerklePath key

[audtlr24]

The oracle get data from panacea by GetStoreData that verify queried data with merkle proof.

GetStoreData use VerifyMembership function used by cosmos/ibc-go.
In VerifiyMemebership, the MerklePath use url path unescaping like below:

// GetKey will return a byte representation of the key
// after URL escaping the key element
func (mp MerklePath) GetKey(i uint64) ([]byte, error) {
	if i >= uint64(len(mp.KeyPath)) {
		return nil, fmt.Errorf("index out of range. %d (index) >= %d (len)", i, len(mp.KeyPath))
	}
	key, err := url.PathUnescape(mp.KeyPath[i])
	if err != nil {
		return nil, err
	}
	return []byte(key), nil
}

Path unescaping is that converting each 3-byte encoded substring of the form "%AB" into the hex-decoded byte 0xAB. It returns an error if any % is not followed by two hexadecimal digits.

Therefore, if we simply do string(key) when creating MerklePath like now, char % can be included in the string, and errors may occur.

To solve this, we can use PathEscape that does inverse transformation of PathUnescape.