As a user I want to find old messages by searching, in encrypted and unencrypted rooms

[dbkr]

• Deploy client-side e2e search indexing on riot-web, implement on mobile

web:

• https://github.com/vector-im/riot-web/issues/11227
• https://github.com/vector-im/riot-web/pull/11125
• https://github.com/matrix-org/matrix-react-sdk/pull/3550
• https://github.com/vector-im/riot-web/issues/11517

[lampholder]

We've agreed that implementing this on Riot Desktop is the only blocker for E2EE by default. We can impl on Riot Mobile ASAP after.