Add chain_getEvents and chain_proveEvents endpoints

[shuse2]

Description

Add framework endpoints as below

chain_getEvents

Req

{
  height: number,
}

Res

{
  events: {
    moduleID: number,
    typeID: number,
    topics: string[],
    data: string,
    index: number,
  }[],
}

If height does not exist, it should return

{
  error: {
    message: `Events at height ${height} is not stored in the node.`,
  }
}

chain_proveEvents

Req

{
  height: number,
  queries: string[],
}

Res

{
  siblingHashes: string[],
  queries: {
    key: string,
    value: string,
    bitmap: string,
  }[]
}

If height does not exist, it should return

{
  error: {
    message: `Events at height ${height} is not stored in the node.`,
  }
}

Acceptance Criteria

• All endpoints are unit tested