Add jql_paged to handle large queries outside of gem

[fuzzkat]

This is an optional addition (last two commits) to PR #468 which adds a method Issue.jql_paged to query by JQL but handles paging outside of the Gem.

Alternatively this could replace the existing Issue.jql method.

freibuis was asking for this to help handle rate limiting. I've not tested it for this purpose, but it should be possible to rescue the exception while looping by doing something like this;

    issues = []
    next_page_token = nil
    loop do
      result = client.Issue.jql_paged(query,
                                      fields: %w[key],
                                      next_page_token:
                                     )

      issues += result[:issues]
      next_page_token = result[:next_page_token]

      break if next_page_token.nil?
    rescue
      # wait and try again
      sleep 1
    end

[d-hansen]

I would support this change. We have tens of thousands of issues and doing a query that retrieved a large amount of them could result in consuming a lot of server memory not to much increases the order complexity of handling them. As such, we do not do any open ended .jql queries. However, if needed, we would definitely take the approach that jql_paged provides, so the system could deal with the found issues in batches.