Implement the blockIndex type of module

[sduchesneau]

Specs

• This module type has no params in its input, has no "initialBlock" and no "output".
• The code for this type of module will simply return an array of strings for a given block.
  Ex: input (block or mapper...) --> output []string
• The output will be saved to disk in a special format using "roaring bitmaps". See https://github.com/streamingfast/bstream/blob/develop/transform/block_indexer.go for an example implementation (or copy it blatantly)

Dependencies

• This depends on proto definitions from Add Substreams Block Filtering to substreams.yaml and protobuf #410

TODO

• make substreams add the indexing module as a dependency in the module tree if a module depends on it through a "blockFilter" parameter.
• Write the code to execute that type of module and gather its outputs
• Write the code to write all those outputs in a roaring bitmap format for the processed range (on tier2)

(this issue does not include the "read" part, i.e. using the index.)

[sduchesneau]

Shipped in https://github.com/streamingfast/substreams/releases/tag/v1.6.0