Fix time_spent GraphQL field type (BigInt?)

The following discussion from !108368 (merged) should be addressed:

• @leetickett-gitlab started a discussion: (+1 comment)

  I enabled the feature flag for me and you @zillemarco

  When I hit the new endpoint i'm getting a 500 from the GraphQL request at the moment.

  Digging in elastic I can see:

  Integer out of bounds: 2409876072 @ timelogs.totalSpentTime (TimelogConnection.totalSpentTime). Consider using ID or GraphQL::Types::BigInt instead.

  I'm going to log some time on this MR then run for today and see what happens 🤞

/cc @zillemarco