Zoekt::Index state :pending -> :initializing

Background

Currently, initial_indexing task in the Scheduling service is written by assuming one ZoektEnabledNamepace can have only one index. But to achieve the indexing for large namespaces we will create multiple indices for one ZoektEnabledNamepace. And for the multiple indices, the initial_indexing task logic is not correct because we are comparing the project counts of a namespace with the zoekt_repositories count in an index. Since one enabled_namespace can have multiple indices this count comparison logic is not correct.

Proposal

Rewrite this task to support the multiple indices for a enablednamespace