Document "Developer options" and remove outdated instructions

[MadLittleMods]

Content

• Document how to access the "Developer options" and what's available there.
• Remove old tips that appear to be copy-pasted from element-android but no longer apply

Motivation and context

Spawning from the new space management UI being demoed in the monthly wrap but being unable to find the feature toggles.

Screenshots / GIFs

N/A, just a docs update

Tests

N/A, just a docs update

Tested devices

• Physical
• Emulator
• OS version(s):

Checklist

• Changes have been tested on an Android device or Android emulator with API 24 N/A
• UI change has been tested on both light and dark themes N/A
• Accessibility has been taken into account. See https://github.com/element-hq/element-x-android/blob/develop/CONTRIBUTING.md#accessibility
• Pull request is based on the develop branch
• Pull request title will be used in the release note, it clearly define what will change for the user
• Pull request includes screenshots or videos if containing UI changes
• You've made a self review of your PR

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[github-actions]

Thank you for your contribution! Here are a few things to check in the PR to ensure it's reviewed as quickly as possible:

• Your branch should be based on origin/develop, at least when it was created.
• The title of the PR will be used for release notes, so it needs to describe the change visible to the user.
• The test pass locally running ./gradlew test.
• The code quality check suite pass locally running ./gradlew runQualityChecks.
• If you modified anything related to the UI, including previews, you'll have to run the Record screenshots GH action in your forked repo: that will generate compatible new screenshots. However, given Github Actions limitations, it will prevent the CI from running temporarily, until you upload a new commit after that one. To do so, just pull the latest changes and push an empty commit.

[MadLittleMods]

Re: CLA

I'm an Element employee and the commit is already using my Element address ⏩

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.36%. Comparing base (5566f10) to head (31ab49c).
⚠️ Report is 29 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #6162      +/-   ##
===========================================
- Coverage    81.37%   81.36%   -0.01%     
===========================================
  Files         2569     2569              
  Lines        69700    69700              
  Branches      8963     8963              
===========================================
- Hits         56716    56712       -4     
- Misses        9650     9655       +5     
+ Partials      3334     3333       -1     

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[jmartinesp]

Thanks for the changes! Since we're already changing this maybe we should also point out modifying developer options can result in the app not working as expected and it should only be done if the user knows what they're doing or if instructed by someone at Element?

[MadLittleMods]

Thanks for the review and merge @jmartinesp and @bmarty 🐡