Use PyUpgrade to use Python 3.6 features

[kaxil]

Use features like f-strings instead of format across the code-base.

More details: https://github.com/asottile/pyupgrade

Features:

• Set literals
• Dictionary comprehensions
• printf-style string formatting
• Unicode literals
• Invalid escape sequences
• .encode() to bytes literals
• super() calls
• "new style" classes
• # coding: ... comment
• Remove unnecessary py3-compat imports
• rewrite mock imports
• if PY2 blocks
• remove six compatibility code
• open alias
• OSError aliases
• typing.NamedTuple / typing.TypedDict py36+ syntax
• remove parentheses from @functools.lru_cache()
• f-strings

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In case of fundamental code change, Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in UPDATING.md.

[kaxil]

@turbaszek Since backport packages are Python 3.6+ too, so upgrading them is fine too, right?

[turbaszek]

@turbaszek Since backport packages are Python 3.6+ too, so upgrading them is fine too, right?

Yes, but I'm afraid this change may cause a lot of merge conflict with currently open PRs. I think we should wait with it for 2.0-alpha, probably apply it at the same moment as black

[kaxil]

@turbaszek Since backport packages are Python 3.6+ too, so upgrading them is fine too, right?

Yes, but I'm afraid this change may cause a lot of merge conflict with currently open PRs. I think we should wait with it for 2.0-alpha, probably apply it at the same moment as black

Yup, this PR can wait :)

[kaxil]

Rebased, so that we can merge it before beta1

[github-actions]

The Workflow run is cancelling this PR. It has some failed jobs matching ^Pylint$,^Static checks,^Build docs$,^Spell check docs$,^Backport packages$,^Provider packages,^Checks: Helm tests$,^Test OpenAPI*.

[github-actions]

The Workflow run is cancelling this PR. It has some failed jobs matching ^Pylint$,^Static checks,^Build docs$,^Spell check docs$,^Backport packages$,^Provider packages,^Checks: Helm tests$,^Test OpenAPI*.

[kaxil]

@turbaszek @XD-DENG This is ready for review, as soon as this is merged. I will quickly rebase and make #9550 pass the test too

[XD-DENG]

LGTM.

A minor question: shall we use the latest v2.7.3?

[kaxil]

Good call, will update