By using a Redis Stream instead of Pub/Sub, the last N frames can be
retained, making debugging easier.

This also updates the Redis client to v8, so that it is possible to
cancel the blocking XRead operation (v7 did not support this).

When the global MQTT integration is enabled, this makes it possible for
users to generate a TLS client-certificate for authentication /
authorization with the MQTT broker.

FUOTA has been moved into an external (optional) component. This means
that ChirpStack Application Server no longer 'intercepts' uplinks
received on FUOTA related FPorts.

Closes #370, #401, #468.

See also:
https://github.com/brocaar/chirpstack-network-server/issues/496.

When using for example Auth0, this makes it possible to configure the
Auth0 logout endpoint (potentially redirecting back to a login page).

This way, the user is not only logged out from the web-interface, but
also from the identity provider.

Closes #519.

This aligns the MQTT configuration with the other components in that an
event and command topic template can be configured. When new events or
commands are introduced, this removes the need add additional
configuration.

This is fully backwards compatible with the old topic configuration.
When `_topic_template` configuration values are found in the
configuration file, these will override the `event_topic_template` and
`command_topic_template` values.

This makes it possible to integrate ChirpStack Application Server with
for example Auth0.com. Using the registration_callback_url it is
possible to automatically provision new users in ChirpStack, create an
organization for the user etc.

In order to add support for OpenID Connect, the username of the user
object has changed into email. Existing users will have their email set
to their username and can continue to login as before. However, when
updating an user, the email field must be updated to a valid email!

Also the option to, as an organization admin, create new users and
assign them to organizations has removed. Assigning new users to an
organization is still possible by the user email address, but the
autocomplete has been removed to avoid privacy issues.

Closes #372.

This is in preparation to support Redis Cluster.

This event indicates that the downlink transmission was acknowledged by
the gateway for transmission.

This adds a configuration value that configures the integration payload
marshaler. Options are:

* json_v3: v3.x JSON format, will be removed but is the current
default for backwards compatibility.
* protobuf: Binary Protobuf encoding.
* json: JSON Protobuf encoding.

This also separates the Protobuf API definitions. These provided by the
chirpstack-api/go package.

This implements the FUOTA building-blocks (remote multicast-setup, app
layer clock sync and fragmentation-session setup) + provides an
implementation of a firmware update engine.

For now, this only implements sending FUOTA deployments to a single
device.