Bug 29672: Increase performance of Koha::Plugins->call

Bug 29672: Increase performance of Koha::Plugins->call

Make use of Koha::Cache::Memory::Lite to avoid hitting the database and
creating plugins object for every call to Koha::Plugins->call

Test plan:
1. Make sure plugins still work by executing
   `prove t/db_dependent/Koha/Plugins/Plugins.t`
2. Run the test script provided in the following patch to see how it
   affects performances

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>