This PR adds estimated sync time to the progress state and changes corresponding test coverage. The idea:

• on the backend side, make a rough estimate based on the elapsed time since sync started and the current sync percentage, check this example:

;(async () => {
const syncStartedAt = Date.now()

// some sync operations
await new Promise(resolve => setTimeout(resolve, 3000))

const progress = 0.23 // 23%, for example
const spentTime = Date.now() - syncStartedAt
const leftTime = (spentTime / progress) * (1 - progress)

// await this.wsEventEmitter.emit(leftTime)
console.log('[leftTime]:', leftTime)
})()

• backend would emit estimated time by WS, also available to get current state using getSyncProgress endpoint, check below a description of returning data
• show on UI estimated time, there need to think about where there's an appropriate place to show more sync info

Breaking changes:
getSyncProgress endpoint and emitProgress WS event return the following data structure:

{
 progress, // as previously value
 syncStartedAt, // null || millisecond timestamp, e.g. `Date.now()`
 spentTime, // null || millisecond difference
 leftTime // null || millisecond difference
}

instead of just progress value as it was before

UI flow:

• show syncStartedAt and spentTime and leftTime only when sync is going on
• if sync catches/throws an error while processing these values can be null. So if progress is not the number don't show the estimated time
• if any variable from syncStartedAt, spentTime, leftTime is null then, for that variable, show Estimating... or something similar instead of just null