Bug 27667: Display a warning for records missing in Elasticsearch

Bug 27667: Display a warning for records missing in Elasticsearch

On "About Koha" page are displayed the numbers of indexed biblios and authorities with ES.
It could be great if we could have comparison with the number of records in the database to display the number of missing records.
In the "System information" tab with the other "Data problems".

If Searchengine has any issue (index count will be -1), we do not
display missing records.

Test plan :
1) Use Elasticsearch searchengine
2) Rebuild all records : koha-elasticsearch --rebuild -d kohadev
3) Go to "About Koha" page and look at System information tab
=> you see no warning
4) On a biblio record delete the MARCXML in biblio_metadata.metadata
5) Rebuild all records : koha-elasticsearch --rebuild -d kohadev
6) Go to "About Koha" page and look at System information tab
=> you see warning : 1 record(s) missing on a total of 435 in indice koha_kohadev_biblios.
7) On a authority record delete the MARCXML in auth_header.marcxml
8) Rebuild all records : koha-elasticsearch --rebuild -d kohadev
9) Go to "About Koha" page and look at System information tab
=> you see warning : 1 record(s) missing on a total of 1705 in indice koha_kohadev_authorities.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>