ESLint Config Migration: Disable max-classes-per-file rule

[filmaj]

Summary

This is a PR that should be merged into #1024 and incrementally addresses #842.

This PR disables the max-classes-per-file rule. There are many situations you would want multiple classes per file, such as a generic errors module or test files that include helper mock classes. As such, I think it would be good to turn this rule off. Alternatively, we can customize the maximum number of classes to something higher.

What do folks think?

Impact

Before

✖ 362 problems (173 errors, 189 warnings)
  76 errors and 0 warnings potentially fixable with the `--fix` option.

After

✖ 359 problems (170 errors, 189 warnings)
  76 errors and 0 warnings potentially fixable with the `--fix` option.

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.

[seratch]

I agree. For this project (and node-slack-sdk project too), we should disable this rule as it does not work for them at all.