Add better description/tooltip to "valid" fields

[Savid]

Validity in the fork choice payload has different values and may not specifically mean the block is "invalid".

Here are prysm validity for example https://github.com/prysmaticlabs/prysm/blob/develop/consensus-types/forkchoice/types.go#L16-L27

At the moment a slot will show yellow if its validity is optimistic and red when its anything other than valid or optimistic.

Might be good to add descriptions everywhere for "valid"/"validity" so its easy and quickly to understand what this field is.