rpc: mark the client tenant using logging tag client-tenant

In the previous change, the logging tag was just "tenant".
This is somewhat confusing/ambiguous with the tenant identity
of the server itself.

Release note: None

pkg/rpc/auth_tenant.go

@@ -444,7 +444,7 @@ func validateSpan(tenID roachpb.TenantID, sp roachpb.Span) error {
 	return checkSpanBounds(rSpan, tenSpan)
 }
 
-const tenantLoggingTag = "tenant"
+const tenantLoggingTag = "client-tenant"
 
 // contextWithClientTenant inserts a tenant identifier in the context,
 // identifying the tenant that's the client for an RPC. The identifier can be