Octodns

* Support for specifying per-zone change thresholds, to allow for zones
where lots of changes are expected frequently to live along side zones
where little or no churn is expected.
* AutoArpa gained support for prioritizing values
* Fix for EnsureTrailingDots reverting value types back to strings which then
failed when rr methods were used on them (e.g. w/octodns-bind)

* Fix env var type handling that was previously fixed in 1.5.1 and then
regressed in 1.6.0.

* Add EnsureTrailingDots processor
* Beta support for custom secret providers added to Manager.

* Improved env variable to parameter type conversion logic, avoid converting
all numbers to float which caused some formatting issues in things that
weren't being careful enough.

* Beta support for Manager.enable_checksum and octodns-sync --checksum Allows a
safer plan & apply workflow where the apply only moves forward if the apply
phase plan exactly matches the previous round's planning.
* Fix for bug in MetaProcessor _up_to_date check that was failing when there was
a plan with a single change type with a single value, e.g. CNAME.
* Support added for config env variable expansion on nested levels, not just
top-level provider/processor keys
* _ChunkedValue ASCII validation added, SPF & TXT
* Re-work value/values handling to always try and do the "right" thing based on
the content, so both singular values and lists will be handled identically
regardless of whether the key is value or values. This may result in
changes/fixes on the first sync after updating IFF you currently have
`values: a-single-thing`, which would have previously been pushed up as bunch
of single character values.
* Record.octodns added to formally make that data "API" and Record._octodns is
deprecated. The latter has been converted to properties that return the
former and emit deprecation warnings.

* Record.lenient property added similar to other common/standard _octodns data
* Processor.process_source_and_target_zones added to support modifying both the
desired and/or existing zones just prior to computing changes.
* Fix bug with Record.copy when values is an empty list []
* Fix an issue in MetaProcessor/Manager.include_meta where include_provider
wasn't correctly taking effect