added minimum block count check

[raduchis]

Reasoning behind the pull request

• the block after the start of epoch block is treated differently and should not be a start of epoch block in any circumstances

Proposed changes

• set a min blocks per epoch so that the next block after a start of epoch blocks is never a start of epoch block

Testing procedure

• allow a start of epoch block to be created and shut down the nodes until the next epoch should start... start the network again and see that at least 4 blocks are in the epoch

Pre-requisites

Based on the Contributing Guidelines the PR author and the reviewers must check the following requirements are met:

• was the PR targeted to the correct branch?
• if this is a larger feature that probably needs more than one PR, is there a feat branch created?
• if this is a feat branch merging, do all satellite projects have a proper tag inside go.mod?