Add optional TTL security field to BGP session product block

docs/includes/glossary.md

docs/vale/styles/config/vocabularies/geant-jargon/accept.txt

gso/cli/imports.py

..._a3177c5f9641_add_optional_ttl_security_to_bgp_session.py

gso/products/product_blocks/bgp_session.py

gso/translations/en-GB.json

...s/l3_core_service/base_create_imported_l3_core_service.py

gso/workflows/l3_core_service/base_create_l3_core_service.py

gso/workflows/l3_core_service/base_modify_l3_core_service.py

gso/workflows/router/validate_router.py

test/fixtures/l3_core_service_fixtures.py

.../workflows/l3_core_service/test_modify_l3_core_service.py