This changes the default behaviour of Synapse to send password reset
emails itself rather than through an identity server. The reasoning
behind the change is to prevent a malicious identity server from
being able to initiate a password reset attempt and then answering
it, successfully resetting their password, all without the user's
knowledge. This also aides in decentralisation by putting less
trust on the identity server itself, which traditionally is quite
centralised.
If users wish to continue with the old behaviour of proxying
password reset requests through the user's configured identity
server, they can do so by setting
email.enable_password_reset_from_is to True in Synapse's config.
Users should be able that with that option disabled (the default),
password resets will now no longer work unless email sending has
been enabled and set up correctly.
move the example email templates into the synapse package so that they can be
used as package data, which should mean that all of the packaging mechanisms
(pip, docker, debian, arch, etc) should now come with the example templates.
In order to grandfather in people who relied on the templates being in the old
place, check for that situation and fall back to using the defaults if the
templates directory does not exist.
