Update store title

According to new PlayStore rules, the title of a mobile application is limited to 30 char (it was 50).

This is OK for our default title: `Element - Secure Messenger` (26 chars). But translations can be longer, for instance in Hungarian, we have `Element - Biztonságos üzenetküldő` (33 chars).

This prevent pushing the store description automatically, and require to edit the long title(s) to reduce their size (see https://github.com/vector-im/element-android/issues/5699#issuecomment-1097768260)

To fix the issue long term, we could consider to update the default title to something shorter, like (in order of preference):
- `Element Messenger`
- `Element`

The translations will then be updated with hopefully shorter lengths.

Other advantage, reducing the title length will limit the ellipsis/multi-line that we can observed on the PlayStore mobile app, when looking for Element:

|Ellipsis|Multi-line - ignore the (Beta) suffix|
|-|-|
|||

### iOS app

It's worth noting than the iOS app is called `Element Messenger`, see https://apps.apple.com/fr/app/element-messenger/id1083446067

So this is probably another argument to rename the Android app to `Element Messenger` for parity!