Review and make sure all 3rd party services are owned by active members

[btlogy]

The project does rely on 3rd party services and some might no longer be controlled by enough active members of the community (e.g.: Cachix is currently blocking CI).

This means those services can break PRs or prevent/delay a release w/o enough contributors having access to the relevant 3rd party provider to fix the problem (e.g.: expired token).

Let's review them all and maybe ensure at least 2 active members are in control.

Tahoe LAFS

Provider	Account	Owner(s)	Status
​GitHub.com	org: Tahoe-LAFS	brian, exarkun, meejah	maybe enough active maintainers?
​app.CircleCI.com	org: Tahoe-LAFS	same as Github	maybe enough active owners?
​app.Cachix.org	org: tahoe-lafs-opensource	exarkun	no active owners and blocking (see #4134)
​hub.Docker.com	org: tahoelafsci	unknown	maybe blocking #4137
​PyPi.org	project: tahoe-lafs	brian, exarkun, meejah	maybe enough active owners?
​test.PyPi.org	project: tahoe-lafs	meejah	only one active owners
​coveralls.io	org or project?	?	maybe enough active owners?

In addition, the same problem can arise in some other projects related to Tahoe-LAFS:

ZFEC

Provider	Account/!Org.	Owner(s)	Status
​GitHub.com	org: Tahoe-LAFS	brian, exarkun, meejah	maybe enough active maintainers?
​app.CircleCI.com	org: Tahoe-LAFS	same as GitHub	maybe enough active owners but likely broken (same as #4098)
​app.Cachix.org	org: tahoe-lafs-opensource	exarkun	no active owners and likely broken (like #4134)
​PyPi.org	project: zfec	exarkun, meejah, sajith, vu3rdd, brian, zooko	maybe enough active owners?
​test.PyPi.org	project: zfec	exarkun, meejah, sajith	supposedly working

Magic Folder

Provider	Account/!Org.	Owner(s)	Status
​GitHub.com	Tahoe-LAFS	brian, exarkun, meejah	maybe enough active maintainers?
​PyPi.org	project: magic-folder	meejah	only one active owners
​test.PyPi.org	project: magic-folder	meejah	only one active owners

Tahoe Capabilities

Provider	Account/!Org.	Owner(s)	Status
​GitHub.com	Tahoe-LAFS	brian, exarkun, meejah	maybe enough active maintainers?
​app.CircleCI.com	Tahoe-LAFS	same as GitHub	maybe enough active owners?
​app.Cachix.org	org: tahoe-lafs-opensource	exarkun	no active owners and likely broken (like #4134)
​PyPi.org	project: tahoe-capabilities	exarkun, meejah	only one active owners
​test.PyPi.org	project: tahoe-capabilities	exarkun	no active owners

Others projects and dev-infrastructure components

Provider	Account	Owner(s)	Status
​Gandi.net	org org users?	brian and meejah?	maybe enough active owners?
​Linode.com	org or users?	brian and meejah?	maybe enough active owners?
​GitLAb.com	org:tahoe-lafs	exarkun, meejah, chris, hacklschorsch, itamars, sajith and shapr	enough active maintainers (but maybe too many owners?)

Alternatively, if one of those 3rd party providers or related projects is not required for Tahoe-LAFS or just obsolete, maybe we should properly archive them (there might be more).