Posthog: Fix inconsistencies on some properties making it hard to properly filter.

[BillCarsonFr]

It is sometime difficult to make posthog filters that work both for mobile and web. The different platforms don't always use the same propertied:

• App Version vs appVersion. Mobile uses the built-in Posthog property App Version($app_version) but web uses a custom appVersion. Web should probably switch to use $app_version

• Crypto Stack: Currently there are 3 different properties for that in posthog cryptoSDK, crypto, cryptoModule. We want to only use cryptoSDK: Rust|Legacy, this properties should be added to all captured events. This is needed to build the "ratio insights". This property should not be reported on the posthog user (identify), we need this property to be per device and on each event.

• Add rust version.

[richvdh]

Related: https://github.com/element-hq/crypto-internal/issues/185

[BillCarsonFr]

Also both EIX and EAX reports the same app name (Element X) => Should have on app name per app for easy breakdown in posthog

[andybalaam]

@BillCarsonFr is this superseded by https://github.com/element-hq/crypto-internal/issues/296 ?