Allow .well-known configuration to override key sharing mode

[jmartinesp]

Type of change

• Feature
• Bugfix
• Technical
• Other :

Content

Fixes #6147 , depends on #6134 .

Variable config outbound_keys_pre_sharing_mode in .well-known configuration of home server will be honoured now, overriding the default value of BuildConfig.outboundSessionKeySharingStrategy.

Motivation and context

See content ^.

Tests

• Set up a home server.
• Add this custom config to the synapse/rest/well_known.py configuration:

"io.element.e2ee": {
  "outbound_keys_pre_sharing_mode": "on_typing" # (or any of on_room_opening, on_typing, disabled)
}

• Create an account in that home server.
• Create or join a room, then do the interaction needed to pre-share the keys (just opening it, typing, etc.).

Tested devices

• Physical
• Emulator
• OS version(s): 12

Checklist

• Changes has been tested on an Android device or Android emulator with API 21
• UI change has been tested on both light and dark themes
• Accessibility has been taken into account. See https://github.com/vector-im/element-android/blob/develop/CONTRIBUTING.md#accessibility
• Pull request is based on the develop branch
• Pull request includes a new file under ./changelog.d. See https://github.com/vector-im/element-android/blob/develop/CONTRIBUTING.md#changelog
• Pull request includes screenshots or videos if containing UI changes
• Pull request includes a sign off
• You've made a self review of your PR
• If you have modified the screen flow, or added new screens to the application, you have updated the test UiAllScreensSanityTest.allScreensTest()

[github-actions]

Unit Test Results

146 files  ±0  146 suites  ±0   2m 50s ⏱️ +18s
236 tests ±0  236 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
788 runs  ±0  788 ✔️ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 2271df9. ± Comparison against base commit 2e1a11e.

♻️ This comment has been updated with latest results.

[yostyle]

LGTM
Clear cache feature doesn't seem affected by this update

[ericdecanini]

LGTM

[github-actions]

Matrix SDK

Integration Tests Results:

• [org.matrix.android.sdk.session]
  = passed=20 failures=0 errors=0 skipped=3
• [org.matrix.android.sdk.account]
  = passed=3 failures=0 errors=0 skipped=2
• [org.matrix.android.sdk.internal]
  = passed=20 failures=2 errors=0 skipped=1
• [org.matrix.android.sdk.ordering]
  = passed=16 failures=0 errors=0 skipped=0
• [org.matrix.android.sdk.PermalinkParserTest]
  = passed=2 failures=0 errors=0 skipped=0