Bump waitress from 1.4.4 to 2.0.0 in /backend

[dependabot]

Bumps waitress from 1.4.4 to 2.0.0.

Changelog

Sourced from waitress's changelog.

2.0.0 (2021-03-07)

Friendly Reminder

This release still contains a variety of deprecation notices about defaults
that can be set for a variety of options.
Please note that this is your last warning, and you should update your
configuration if you do NOT want to use the new defaults.
See the arguments documentation page for all supported options, and pay
attention to the warnings:
https://docs.pylonsproject.org/projects/waitress/en/stable/arguments.html
Without further ado, here's a short list of great changes thanks to our
contributors!
Bugfixes/Features

• Fix a crash on startup when listening to multiple interfaces. See Pylons/waitress#332

• Waitress no longer attempts to guess at what the server_name should be for a listen socket, instead it always use a new adjustment/argument named server_name.

  Please see the documentation for server_name in https://docs.pylonsproject.org/projects/waitress/en/latest/arguments.html and see Pylons/waitress#329

• Allow tasks to notice if the client disconnected.

  This inserts a callable waitress.client_disconnected into the environment that allows the task to check if the client disconnected while waiting for the response at strategic points in the execution and to cancel the operation.

  It requires setting the new adjustment channel_request_lookahead to a value larger than 0, which continues to read requests from a channel even if a request is already being processed on that channel, up to the given count, since a client disconnect is detected by reading from a readable socket and receiving an empty result.

  See Pylons/waitress#310

• Drop Python 2.7 and 3.5 support

... (truncated)

Commits

• 4b6b583 Prep 2.0.0
• c159853 Prep 2.0.0b1
• 19793c0 Merge pull request #332 from Pylons/fix-default-logging
• 994b556 add changelog for #332
• e5d4437 fix a crash in the MultiSocketServer startup and re-enable startup messages
• 665240e Prep 2.0.0b0
• 38a1186 Move CHANGES to HISTORY
• 9674f3e Merge pull request #329 from Pylons/cleanup/server-name
• 8245c18 Add changelog entry for server_name
• 88b0073 Add documentation for server_name
• Additional commits viewable in compare view

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[dependabot]

Superseded by #70.