feat: save chain metadata to files instead of database

[hanabi1224]

Summary of changes

Changes introduced in this pull request:

As part of #2292

• Save genesis block header and heaviest tipset keys to files instead of database

Reference issue to close (if applicable)

Closes

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

[LesnyRumcajs]

@hanabi1224 Could you please write a short note on why we want to save metadata for files instead of the database in this PR? It's nice to have some trace, for the well-being of future us, trying to understand the reason behind changes.

[hanabi1224]

@LesnyRumcajs Sure, the idea is to only save block data which are content-addressed to the DB, so that we could

• make GC logic easier, without taking care of non blockchain data
• benefit from performance optimizations in paritydb. (see doc about preimage and uniform)
• more reason in Remove block validation meta-data from the blockstore #2642