Disable typescript-eslint/no-explicit-any in internal code of web-api

[seratch]

Summary

This pull request disables eslint warnings about the usage of any type in the internal code of web-api package. I think that disabling these should be safe enough.

> @slack/web-api@6.4.0 lint /Users/ksera/github/node-slack-sdk/packages/web-api
> eslint --ext .ts src


/Users/ksera/github/node-slack-sdk/packages/web-api/src/WebClient.ts
   83:34  warning  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any
  381:48  warning  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any
  381:62  warning  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any
  427:28  warning  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any
  448:73  warning  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any
  452:60  warning  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any
  482:37  warning  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any
  482:53  warning  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any
  511:42  warning  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any

/Users/ksera/github/node-slack-sdk/packages/web-api/src/errors.ts
  41:10  warning  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any

/Users/ksera/github/node-slack-sdk/packages/web-api/src/methods.ts
  2078:14  warning  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any
  2081:24  warning  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any

✖ 12 problems (0 errors, 12 warnings)

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.