cli: speedup the `swh` cli command startup time

by moving import statements in functions. Also move the definition of StepOption in swh.graph.cli since it's purely a click dedicated class.

Related to swh-environment#2575 (closed).

---

Migrated from D3910 (view on Phabricator)

Some references in the commit message have been migrated:

• T2575 is now swh-environment#2575 (closed)

Build is green

Patch application report for D3910 (id=13769)

Rebasing onto 8c937da2...

Current branch diff-target is up to date.

Changes applied before test

commit 4a643fcce445cc5efc3d1442092578e962363498
Author: David Douard <david.douard@sdfa3.org>
Date:   Thu Sep 10 10:56:11 2020 +0200

    cli: speedup the `swh` cli command startup time
    
    by moving import statements in functions. Also move the definition
    of StepOption in swh.graph.cli since it's purely a click dedicated
    class.
    
    Related to swh/devel/swh-environment#2575.

See https://jenkins.softwareheritage.org/job/DGRPH/job/tests-on-diff/25/ for more details.

mentioned in merge request !75 (closed)

Merge request was accepted

approved this merge request

Merge request was merged

closed