Update development dependency - Twine to v3.2.0

Twine version < 2.0 was reported has a security vulnerability

From Twine version 2.0+, it requires Python 3.6, but doesn't seem to
have other breaking changes.

Reference:

- https://github.com/pypa/twine/issues/491
- https://twine.readthedocs.io/en/latest/changelog.html

manager: error when an alias zone is synced without its source

Signed-off-by: Marc 'risson' Schmitt <marc.schmitt@risson.space>

Updated document for unsafe thresholds

Ignore UltraDNS records with unsupported rrtypes and log warning.

Co-authored-by: Ross McFarland <ross@github.com>

Replace some nbsp chars that have slipped into manager.py somehow

Update links to octodns/octodns

fix: error in gandi.py

Also add Python v3.6, v3.8 on GitHub Actions for test

Unlike Python v2 as v2.7 is 10 years old, Python v3 has more versions
alive amoung us, it'll be great if they will all be tested.

Fix _is_valid_dkim_key for Python 3.9 compatibility in OVH provider

Improve ALIAS, CNAME, DNAME & PTR record FQDN validation

base64.decodestring was deprecated and removed in Python 3.9 in favour of
decodebytes (See https://bugs.python.org/issue39351 )

cc #84 #628

Use fqdn package to help verify if the record value is really valid.

The original behavior will treat value like `_.` or `.` be a valid
record, which is strange, and the real world may not have those use
cases at all.

The RFC documents are pretty long, as I didn't read them all or enough
to tell should it be valid or not by the spec, so I opened issue #612 to
discuss this case and got a positive response from the main maintainer
to have the change.

Close #628

PowerDNS: Support pre-release versions

This commit strips any superfluous -alphaN (or beta or rc) from the
version number's minor number so it can be cast to an int. This will
allow octodns to sync to/from PowerDNS pre-releases.

Fix name length validation

Closes #626

Add CAA record support to AxfrSource/ZoneFileSource

v0.9.11 version bump and CHANGELOG update