Block beacon header sync until global pivot is updated

[marcindsobczak]

Fixes #6304

Changes

• block a start of beacon header sync until global pivot is updated

Beacon header sync can be initialized only when global pivot is already set, otherwise it might result in conflicting pivots and a deadlock

Types of changes

What types of changes does your code introduce?

• Bugfix (a non-breaking change that fixes an issue)
• New feature (a non-breaking change that adds functionality)
• Breaking change (a change that causes existing functionality not to work as expected)
• Optimization
• Refactoring
• Documentation update
• Build-related changes
• Other: Description

[kamilchodola]

While fixing that did you managed to find a proper reproduction for that? For me it is quite random and did not noticed what exactly I need to do to make it fully reproducible.

[marcindsobczak]

@kamilchodola I didn't reproduced an issue, but I reproduced the root cause of an issue - setting beacon pivot and starting beacon header sync before setting global pivot. It is still working fine most of the time, but rarely pivots are conflicting and it is breaking the node - I didn't reproduced that part. This PR is fixing the root cause, so we will not have this issue anymore

[MarekM25]

@kamilchodola @marcindsobczak While fixing the block production issue, I encountered a few syncing issues with beacon headers. I think this can happen when your CL is not close to the head and needs to catch up to the tip of the chain.

[MarekM25]

PR looks good, but @kamilchodola it will require some testing for sure. I guess a good idea is to restart CL (lighthouse)/EL a few times and trigger a new beacon sync in this way.

@marcindsobczak think about if it can be covered somehow by integreation tests