Improve db storage in chain connector plugin

[!shan]

Expected behavior

It should be easy to retrieve any data from the chain connector plugin using endpoints

Actual behavior

When no CCU is sent over a long period of time, the data stored grows linearly and the endpoints currently simply expose the whole array of data that leads to memory issues.

Steps to reproduce

• Sync a node with Chain connector plugin enabled which is more than 500 blocks behind the current height and check chainConnector_getBlockHeaders endpoint if the data is saved for all the heights.

Which version(s) does this affect? (Environment, OS, etc...)

6.0.1