enhancement(observability): API batch support + tests (#5004)

* batch events processed total

Signed-off-by: Lee Benson <lee@leebenson.com>

* commentary

Signed-off-by: Lee Benson <lee@leebenson.com>

* add subscriptions

Signed-off-by: Steven Hall <sghall@protonmail.com>

* formatting

Signed-off-by: Steven Hall <sghall@protonmail.com>

* tests

* fixes

Signed-off-by: Lee Benson <lee@leebenson.com>

Co-authored-by: Steven Hall <sghall@protonmail.com>