Zoekt::Repository state :initializing/:ready -> :failed

Background

There may be cases where some projects just can't indexed due to any reason. For eg: if a project is huge we can't index it under a given timeout. In this case, it will always keep the node locked for indexing which will eventually fail.

Proposal

Add a new smallint column retries_left. Decrement the count whenever the indexing task is set to failed. Move the Search::Zoekt::Repository record to failed when the retries_left reaches 0. Do not index the failed repository. Set the retries_left back to default(10) when the indexing gets successful