Bug 26641: Optimize CatalogModuleRelink lookup

Bug 26641: Optimize CatalogModuleRelink lookup

This patch moves the CatalogModuleRelink lookup outside the loop to
improve performance (especially for large databases), and includes a
tester friendly test plan.

Test plan:
0. Using koha-testing-docker
1. koha-shell -c "./misc/link_bibs_to_authorities.pl -l --test" kohadev
2. Note 436 bibs checked, 1315 headings linked, 676 headings unlinked
3. koha-shell -c "./misc/link_bibs_to_authorities.pl -l --test -g 700" kohadev
4. Note 436 bibs checked, 248 headings linked, 111 headings unlinked
5. Note output appear to all be names (rather than subjects or other authorities)
6. Note also that the 2nd run with -g 700 is almost 2x faster than without

Signed-off-by: Andreas Roussos <a.roussos@dataly.gr>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>