[exporterhelper] Refactor persistent storage size backup

[dmitryax]

Currently we have this logic to persist the current queue size every 10 writes to ensure it can be restored after a crash. The problem that it's not reliable and can lead to sizing problems.

Instead, we should write all the information every time under one key: start/stop/inprogres/size.

[malus2077]

Hi! I'd like to work on this issue. Could you please assign it to me? Thanks!

[sincejune]

@malus2077 Assigned to you.

[malus2077]

I’ve opened PR #13047 to address this. Please have a look when you get a chance.