Bug 36725: Add Current publication frequency 310$a to Elasticsearch index mappings

Bug 36725: Add Current publication frequency 310$a to Elasticsearch index mappings

Test plan:
1. Start up KTD with Elasticsearch: ktd --es8 up

2. Apply this patch and restart all services (restart_all)

3. Reset the mappings: Administration > Catalog > Search engine configuration (Elasticsearch) > Reset mappings (at the bottom of the page)

4. Reindex: koha-elasticsearch --rebuild -d -b -a kohadev

5. Alternative to steps 3 and 4: reset_all

6. Add a new record using the default framework and put a term in 310$a, such as 'Annual'.

Sponsored-by: Education Services Australia SCIS
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>