enh: Standardize Logic and Admin Control to list events on index

[maze-runnar]

Fixes (Partly) #4697

Short description of what this resolves:

We have tried different ways to control events automatically that we want to show up on the front page. It is time to standardize a logic how events show up on the front page.

1. Featured Events

• This is easy. Any event that is switched to "Featured Event" by admins is listed here.

2. Upcoming Events

• up to 21 events should be listed here
• admins should have the option to move any event without restrictions to the top of this line by switching events to "Promoted Events" in the event admin panel
• promoted events should always show up on the top of "Upcoming Events"
• other than that there are the following requirements for events to show up here (if they are not promoted). The event should have
  • location or online link and a date
  • a minimum of 8 paid tickets sold or be a paid pro-event
  • Once tickets are sold out the event should not be promoted to the front page anymore. Once the ticket sales period has ended the event should not be promoted to the front page anymore
  • an event image

3. Call for Speakers

• Up to 12 events should be listed here and there should be a "more link" below to show more events on the cfs page if there are more events
• Events listed here on top of the queue should be "Pro Events"
• Non-Pro Events can be listed here as well, if they have
  • Call for Speakers
  • a location or online link and a data
  • an event image

Checklist

• I have read the Contribution & Best practices Guide.
• My branch is up-to-date with the Upstream development branch.
• The acceptance, integration, unit tests and linter pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

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[codecov]

Codecov Report

Merging #4780 into development will increase coverage by 0.06%.
The diff coverage is 72.72%.

@@               Coverage Diff               @@
##           development    #4780      +/-   ##
===============================================
+ Coverage        23.23%   23.30%   +0.06%     
===============================================
  Files              480      480              
  Lines             5039     5047       +8     
  Branches             9        9              
===============================================
+ Hits              1171     1176       +5     
- Misses            3867     3870       +3     
  Partials             1        1              

Impacted Files	Coverage Δ
app/controllers/index.js	83.33% <72.72%> (-7.58%)	⬇️

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[maze-runnar]

this is done in another PR so closing this one.