[AIRFLOW-1443] Update Airflow configuration documentation

[allisonwang]

Dear Airflow maintainers,

Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!

JIRA

• My PR addresses the following Airflow-1443 issues and references them in the PR title.

Description

• Here are some details about my PR, including screenshots of any UI changes:
  This PR updates Airflow configuration documentations to include a recent change to split task logs by try number [AIRFLOW-1332] Split logs based on try number  #2383.

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:

Commits

• My commits all reference JIRA issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

@aoen

[mention-bot]

@allisonwang, thanks for your PR! By analyzing the history of the files in this pull request, we identified @jlowin, @boristyukin and @sekikn to be potential reviewers.

[aoen]

For grammar and because try number is really no more special than dag_id/execution_date (it's part of the key), let's changes this to:
Logs are stored in the log folder as dag_id/task_id/execution_date/try_number.log.

[aoen]

cc @bolkedebruin

[codecov-io]

Codecov Report

Merging #2467 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2467   +/-   ##
=======================================
  Coverage   69.98%   69.98%           
=======================================
  Files         146      146           
  Lines       11446    11446           
=======================================
  Hits         8011     8011           
  Misses       3435     3435

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d9109d6...815f67f. Read the comment docs.

[bolkedebruin]

Please also update UPDATING.md. People that do log rotation from the OS will need to reconfigure. Please also correct the commit message to reflect what you are updating in the docs.

[saguziel]

maybe add some angle brackets so it is clear they are templated variables, itwill read a bit better

[aoen]

LGTM