Add supervisor to Auth container image

[nvaatstra]

Short description

This PR adds supervisor to the Auth container image. Tini is still in place as default init process, but supervisor can be used for scenarios where more advanced process management has benefits.

Scenarios where this might be beneficial include:

• Running multiple processes (ie: auth + ixfrdist) within a single container
• Kubernetes: Automating restarts of a process (ie: ixfrdist) within a container when a mounted configmap containing the process' configuration is observed to have been changed (without restarting the container itself)

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[coveralls]

Pull Request Test Coverage Report for Build 7207638419

Warning: This coverage report may be inaccurate.

We've detected an issue with your CI configuration that might affect the accuracy of this pull request's coverage report.
To ensure accuracy in future PRs, please see these guidelines.
A quick fix for this PR: rebase it; your next report should be accurate.

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 105 unchanged lines in 10 files lost coverage.
• Overall coverage increased (+0.002%) to 57.68%

---

Files with Coverage Reduction	New Missed Lines	%
pdns/backends/gsql/gsqlbackend.hh	2	97.71%
pdns/tcpiohandler.cc	2	66.5%
pdns/rcpgenerator.cc	3	90.41%
pdns/iputils.cc	4	45.31%
pdns/packethandler.cc	4	73.2%
pdns/dns.hh	7	75.0%
ext/luawrapper/include/LuaContext.hpp	8	13.79%
pdns/recursordist/test-syncres_cc1.cc	12	88.83%
modules/lmdbbackend/lmdbbackend.cc	14	72.43%
pdns/dnsparser.cc	49	84.74%

Totals
Change from base Build 7184070321:	0.002%
Covered Lines:	107564
Relevant Lines:	155148

---

💛 - Coveralls

[Habbie]

great! one doc formatting nit, that I'll apply now