Airflow 2.0.0b3 snapshot ready for testing.

[Ash Berlin-Taylor <as...@apache.org>]

It's Airflow 2.0.0 beta time!

This /*might*/ be the last beta before release candidate -- so now is 
your time to test this thoroughly if you are able. Remember, we are 
aiming to have RC available by the week of 7th December, so in order to 
try and have as few release candiates as possible we are going to slow 
down/stop all together adding any new features in to this release.

The beta latest snapshot is available at:

<https://dist.apache.org/repos/dist/dev/airflow/2.0.0b3/>

*apache-airflow-2.0.0b3-source.tar.gz* is a source release that comes 
with INSTALL instructions.

*apache-airflow-2.0.0b3-bin.tar.gz* is the binary Python "sdist" 
snapshot.

*apache_airflow-2.0.0b3-py3-none-any.whl* is the binary Python wheel 
snapshot.

Once again, this snapshot *has* been pushed to PyPi.

(The new features added below are all small code changes.)

_Major features since beta2:_

New features:
* Add description field to connection (#10873)
* Use different deserialization method in XCom init_on_load (#12327)
* Make nav fully accessible y keyboard, fix mobile nav menus (#12351)
* Add metric for scheduling delay between first run task & expected 
start time (#9544)
* Create DAG-level cluster policy (#12184)

Improvements:

* UI: Improve the layout of TI modal when browser at narrower widths 
(#12456)
* PR to add 'files' to template-fields in EmailOperator class (#12428)
* JSON Response is returned for invalid API requests (#12305)
* Make K8sPodOperator backwards compatible (#12384)
* Don't display DAG docs when None (#12415)
* Simplify using XComArg in jinja template string (#12405)
* Remove inapplicable configuration section [ldap] (since 2.0.0) 
(#12386)
* Add info log message about duration taken to load plugins (#12308)
* Manage Flask AppBuilder Tables using Alembic Migrations (#12352)
* UI: Improve presentation of DAG Docs (#12330)
* Wait option for dagrun operator (#12126)
* Use default view in TriggerDagRunLink (#11778)
* Handle naive datetimes in REST APIi (#12248)
* Unify user session lifetime configuration for webserver (#11970)

Bug fixes:

* Fix typo in migrations: RESOURCE_DAGS to RESOURCE_DAG. (#12460)
* UI: Fix bug in server timezone indicator (#12447)
* Fix issues with Gantt View (#12419)
* Proper exit status for failed CLI requests (#12375)
* Check for TaskGroup in _PythonDecoratedOperator (#12312)
* Reject 'connections add' CLI request if URI provided is invalid 
(#12370)
* Reorder Database Migrations (#12362)
* Refactor root logger handling in task run (#12342)
* Bugfix: REST API Variables update endpoint returns 204 No Content 
(#12321)
* UI: Fix/Enhancement: Disable forms and communicate to user when no 
DAG Runs (#12320)
* UI: Get all "tags" parameters not just one (#12324)
* Make dag_id, task_id, and execution_date nullable in event log schema 
(#12287)
* Don't wrap warrning messages when stderr is not a TTY (#12285)
* Don't treat warning message as rich formatting codes. (#12283)
* UI: Fix pause/unpause toggle to display failed state when 
unsuccessful (#12267)
* UI: Conditionally update button URL only when it is present (#12268)

Docs:

* Cleanup requirements in README a bit (#12446)
* Synchronization of supported K8S version (#12443)
* Show all Providers in Docs (#12363)
* Restructure documentation for releasing Airflow/Providers (#12350)
* Fix Sample CLI commands for upgrading to 2.0 (#12349)
* Docs installation improvements (#12304)
* Remove providers imports from core examples (#12252)

Misc/Internal:

* Move setup properties out of setup.py in to setup.cfg (#12417)
* Change log level for User's session to DEBUG (#12414)
* Adds mechanism for provider package discovery. (#12383)
* Add success/failed sets to State class (#12359)
* Enable protection for v1-10-stable branch (#12343)
* Fix prod image build (#12314)
* Remove deprecated Elasticsearch Configs (#12296)
* Remove deprecated BashTaskRunner (#12295)
* Added k9s as integrated tool to help with kubernetes testing (#12163)
* Providers in extras are properly configured and verified (#12265)

For changes to the providers, please see the individual provider readme.
-ash