Add conversations.requestSharedInvite.list API support

[filmaj]

FYI @seratch & @WilliamBergamin

We will need to add support soon for this API: https://api.slack.com/methods/conversations.requestSharedInvite.list

This closely relates to #1365

This document shows the necessary requirements in terms of Slack plan (enterprise grid) and settings (specific enterprise Slack Connect settings): https://api.slack.com/automation/governing-slack-connect-invites

Once you have the above set up, then when a non-admin / non-owner user (this part tripped me up!) sends a Slack Connect invite, you can use the list API to then list out these to-be-approved SC invites. I tested this out by having a regular grid user open up a channel's settings -> Settings tab -> Slack Connect invite.

@seratch this PR is definitely insufficient to add support for this API to the java SDK - my apologies. When I have a moment, I will review past PRs that added new APIs to this repo and copy the approach. If you have any additional pointers for this, let me know and I can address it tomorrow. In the mean time, this PR at least unblocks me from getting a PR for this API ready in the node-slack-sdk repo. EDIT: I've added some more to this PR but I am still missing the ListResponse class; since the response structure is a bit more complicated than the simple cases, I am not sure how to exactly proceed - your guidance would be appreciated. Feel free to push to this PR if it's something you can address directly easier, too.

[codecov]

Codecov Report

Attention: Patch coverage is 86.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 74.55%. Comparing base (11e46d0) to head (353521f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...java/com/slack/api/methods/RequestFormBuilder.java	80.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1382      +/-   ##
============================================
+ Coverage     74.52%   74.55%   +0.02%     
- Complexity     4324     4329       +5     
============================================
  Files           472      472              
  Lines         13491    13506      +15     
  Branches       1377     1378       +1     
============================================
+ Hits          10054    10069      +15     
+ Misses         2624     2623       -1     
- Partials        813      814       +1     

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[seratch]

@filmaj Thanks for working on this! I've completed the remaining changes and needed adjustment!