Rename StatusResolver to AllowedStatusesResolver

What does this MR do and why?

As part of the first iteration of the configurable work item statuses initiative and in response to this MR feedback, we would like to make it easier to distinguish between Resolvers::WorkItems::Widgets::AllowedStatusesResolver and Resolvers::WorkItems::BulkStatusResolver.

References

• Rename ::StatusResolver to ::AllowedStatusesResolver
• BE: Implement GraphQl APIs
• Work items custom status design document
• Configurable Work Item Statuses Epic

Screenshots or screen recordings

backend changes only.

How to set up and validate locally

• Refer to testing instructions and queries from this MR.

MR acceptance checklist

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