Riot: clarify the 'deactivate account' UX

[ara4n]

I don't think we even have a deactivate button on iOS or Android today, which obviously should be added as part of this.

This has two parts:

• [ ] Improve wording explaining what deactivation means
• [ ] Add a checkbox to request a GDPR erasure at the point of deactivation, which should then hit whatever the API synapse provides for GDPR erasure will be.

[manuroe]

The current UI/UX for account deactivation from the settings page on riot-web is:

[manuroe]

The CS API endpoint is https://matrix.org/docs/spec/client_server/r0.3.0.html#post-matrix-client-r0-account-deactivate.

[lukebarnard1]

Most up-to-date wording spec is https://docs.google.com/document/d/1n0YmfdT8y28cVyWkRzeradSFKZrX8lYADhFBUbGU_LQ/edit#

of which https://github.com/matrix-org/matrix-react-sdk/pull/1922 is the most up-to-date Riot web implementation:

[manuroe]

@SBiOSoftWhare , @bmarty , here is how the erase option is implemented in matrix-js-sdk: https://github.com/matrix-org/matrix-js-sdk/pull/649/files#diff-7ecbd1742c9fa46478efe534d035eb28R341