* Move gossip modules to solana-gossip
* Update Protocol abi digest due to move
* Move gossip benches and hook up CI
* Remove unneeded Result entries
* Single use statements
1. Allow the validator bootstrap code to specify the minimal snapshot download speed. If the snapshot download speed is detected below that, a different RPC can be retried. The default is 10MB/sec.
2. To prevent spinning on a number of sub-optimal choices and not making progress, the abort/retry logic is implemented with the following safe guards:
2.1 at maximum we do this retry for 5 times -- this number is configurable with default 5.
2.2 if the download in one notification round (5 second) is more than 2%, do not do retry -- it is not as bad anyway.
2.3 if the remaining estimate time is less than 1 minutes, do not abort retry as it will be done quickly anyway.
2.4 We do this abort/retry logic only at the first notification to avoid wasting download efforts -- the reasoning is being opportunistic and too greedy may not achieve overall shorter download time.
3. The download_snapshot and download_file is modified with the option allowing caller to notified of download progress via a callback. This allows the business logic of retrying to the place it belongs.
* Add blockstore-root-scan for api nodes on boot
* Ensure cluster-confirmed root and parents are set as root in blockstore in load_frozen_forks()
* Plumb rpc-scan-and-fix-roots validator flag
* purge_old_snapshot_archives is changed to take an extra argument 'maximum_snapshots_to_retain' to control the max number of latest snapshot archives to retain. Note the oldest snapshot is always retained as before and is not subjected to this new options.
* The validator and ledger-tool executables are modified with a CLI argument --maximum-snapshots-to-retain. And the options are propagated down the call chains. Their corresponding shell scripts were changed accordingly.
* SnapshotConfig is modified to have an extra field for the maximum_snapshots_to_retain
* Unit tests are developed to cover purge_old_snapshot_archives
* AccountSecondaryIndexes.include/exclude
* use normal scan if key is not indexed
* add a test to ask for a scan for an excluded secondary index
* fix up cli args