Fix base-path handling in key insert (#7775)

This fixes the handling of base-path when using `key insert`. Before
the base-path wasn't setup correctly, as done when starting a node. This
resulted in putting the keys into the wrong directory. This pr fixes
this by creating the correct base-path/config dir for the keystore.
Besides that it also removes the insert command from `subkey` as it
doesn't make that much sense. If requested, we could bring it back later.

substrate/client/cli/src/error.rs

@@ -59,9 +59,6 @@ pub enum Error {
 		expected: usize,
 	},
 
-	#[error("The base path is missing, please provide one")]
-	MissingBasePath,
-
 	#[error("Unknown key type, must be a known 4-character sequence")]
 	KeyTypeInvalid,