fix false positive POI (graphprotocol#3951)

add 'send_all_block_headers' param for blockHandler

news: Release v0.28.0

graph: Remove a possible crash from the polling block stream

PollingBlockStreamContext.parent_ptr contained an expect that failed if the
provider didn't return a parent pointer. Turn that panic into an error.

store: Lock subgraph_deployment to coordinate with pruning

This is a bit of PR 3898 so that `graphman prune` can be used on the perf
cluster

Merge branch 'master' into stepd/firehose_gzip

gate gzip on firehose behind 'compression' config feature

firehose: timeout on `block_ptr_for_number`

Stable release v0.27.0 (control)

news: Release 0.27.0