[BCI-887] Solana HeadTracker Integration

[yongkangc]

This PR attempts to integrate the chain specific headtracker on the EVM generalised platform based on the Epic ticket on chain specific headtracker.

This is a POC on how likely the generalised headtracker could be implemented in a chain specific context, will remain as a draft PR for now given all changes that are likely to happen with the Headtracker.

Changes:

• common folder pkg/common is added to replicate imports on chainlink-relay
• Config for Headtracker has been changed. The changes for core can be seen here [BCI-1422]Added Values for Solana Headtracker Config chainlink#9572
  • Note that the changes for core has to be implemented and bumped up for the integration of addition of config values.
• Added Solana head
• Added poller client for head

Note:

• Core imports needs to be replaced with a relay import. This is because of the time constraint for the POC project, therefore I made the choice to directly import the necessary components from core. into the Solana repo instead of relying on chain-relay imports.
  • Currently this is the PR for relay imports: Added Generalised Headtracker Components chainlink-common#123

References:

• Epic Ticket
• Design Proposal on Generalised Headtracker

[yongkangc]

Integration completed, All tests passing

cc @aalu1418 @prashantkumar1982

[prashantkumar1982]

add this:

if h == nil {
	return nil
}

[prashantkumar1982]

Might be able to optimize logic here.
For example, if slotNum is higher than current slot, then return Hash{}. This way, you return quicker.