make PAGE_SIZE configurable for Slack API list calls

[kintarowins]

Summary

Describe the goal of this PR. Mention any related Issue numbers.

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[CLAassistant]

All committers have signed the CLA.

[seratch]

I know this approach is a pretty easy way to make this work. However, now that the value is no longer a constant, we may want to use an instance filed like @page_size over a class field plus replace the references to SlackClient.PAGE_SIZE in the code.

[kintarowins]

Thanks, yeah I was thinking that too, needed someone to confirm my own doubt. I used @apiPageSize to follow existing camelCase naming convention.

[seratch]

@kintarowins Thanks a lot for promptly updating the PR. Right now, I'm a bit busy for other tasks but I will be checking if this change works as we expect.

By the way, can you sign our CLA (see the above bot message for details)? 🙇 Without it, we are unable to merge your change.

[kintarowins]

Signed. I changed default page size to 200 too, what do you think or should it be higher?

[seratch]

@kintarowins Thanks for signing it. Regarding the page size, I am reluctant to change the default value for keeping backward compatibility. Your change enables developers to customize the size. Let's keep the default as-is.

I did not have time to do some tests today but I'll check this sometime this week.

[seratch]

I just verified if your change works with my Hubot example apps. Before merging this pull request, I will migrate the CI builds to GitHub Actions.

Thanks for your contribution!

[codecov]

Codecov Report

Merging #612 (476fca6) into main (00edee0) will decrease coverage by 0.41%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main     #612      +/-   ##
==========================================
- Coverage   84.23%   83.82%   -0.42%     
==========================================
  Files           6        6              
  Lines         406      408       +2     
  Branches       90       91       +1     
==========================================
  Hits          342      342              
- Misses         37       38       +1     
- Partials       27       28       +1     

Impacted Files	Coverage Δ
src/bot.coffee	73.98% <ø> (ø)
src/client.coffee	89.56% <50.00%> (-1.59%)	⬇️

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