Custom consensus support for conduit and indexer

## Problem

Custom consensus is allowed in the algod, but the conduit and indexer cannot connect to such node.

## Solution

Custom consensus is allowed in the algod, but the conduit and indexer cannot connect to such node as the sync of the consensus specs is not implemented yet. Meanwhile the solution is to copy the consensus file to the indexer and conduit, but for this some functions must be copied from the go-algorand repository to be shared among the conduit and indexer repos.

## Dependencies

None

## Urgency

We are using custom consensus for years now, and we make the pull requests to the algorand code base which was not approved yet. Meanwhile we are running on custom built conduit and indexer docker images.

It would be nice if our work is included in the general repo, but we can live with this situation.

## Related pull requests

https://github.com/algorand/go-algorand-sdk/pull/756
https://github.com/algorand/indexer/pull/1678
https://github.com/algorand/conduit/pull/190

Obsolete pull requests:
https://github.com/algorand/go-algorand-sdk/pull/625
https://github.com/algorand/indexer/pull/1631
https://github.com/algorand/indexer/pull/1327
https://github.com/algorand/indexer/pull/1041
https://github.com/algorand/conduit/pull/162