Page large messages in gkctl

The scripts shipped with `gkctl` (i.e. scripts in [folder `gkctl/scripts`](https://github.com/AltraMayor/gatekeeper/tree/master/gkctl/scripts)) will have their output truncated if the output is larger than 64KiB due to the maximum size of the messages of the dynamic configuration block. While this is not a problem for most scripts, it is an issue for scripts `show_fib.lua` and `show_fib6.lua` when routing tables are large.

Increasing the limit of the messages of the dynamic configuration block is not a solution because routing tables are essentially unbounded. And this limit exists to guarantee that the dynamic configuration can bound its operations. Thus, some form of paging large messages is needed.

A possible solution is to enhance `gkctl` to receive parameters from the command line that are passed to the Lua scripts. That is, the Lua scripts would actually be templates that will have their parameters replaced before being passed to the dynamic block. This way, one can pass a parameter that says from where the dump of a routing table begins. Passing parameters to Lua scripts may even find other applications.

Once parameters for scripts are available, `gkctl` could support some mechanism to run scripts multiple times with different parameters to get the whole routing table with a single call of `gkctl`.