fix indexer nextKey pagination

[dib542]

the pagination options currently accepted are

interface PaginationRequest {
  key?: string;
  offset?: number;
  limit?: number;
  before?: number; // unix timestamp
  after?: number;  // unix timestamp
}

interface PaginationResponse {
  next-key: string | null;
}

which is meant to reflect the pagination options available in Cosmos (see any list endpoint in https://docs.cosmos.network/swagger)

interface CosmosPaginationRequest {
  key?: string;
  offset?: number;
  limit?: number;
  count_total?: boolean;
  reverse?: boolean;
}

interface CosmosPaginationResponse {
  next_key: string | null;
  total?: string;
}

but there are issues that:

• the pagination key (pagination.nextKey) returned from a paginated request does not keep the previous limit option from the original request
• the next-key name returned doesn't match Cosmos's default next_key name.