Fix import channel in Postgresql

[jredrejo]

Summary

When importing channel data, psycopg2 execute_values function was used. This function code converts to bytes all the strings in order to have a better performance.
However, converting an utf-8 char to byte results in more than one byte, making some strings unfit in the maximum number of chars of a column limit.

This PR:

• Replaces the use of execute_values by executemany
• As sqlite does not applies the column char limit, ensures limit is applied to data before is inserted in Postgresql

Note: I had to cherry-pick the commit from #12466 to fix docs builds in GH

References

Closes: #11780

Reviewer guidance

Do tests pass?
In order to test the fix, this channel was failing and can be used in a kolibri installation using PG:
kolibri manage importchannel network --baseurl=https://studio.learningequality.org 07cd1633691b4473b6fda08caf826253

Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

PR process

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.17.3a0.dev0_git.12.g1aadc9b9.pex
Windows Installer (EXE)	kolibri-0.17.3a0.dev0+git.12.g1aadc9b9-windows-setup-unsigned.exe
Debian Package	kolibri_0.17.3a0.dev0+git.12.g1aadc9b9-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.17.3a0.dev0+git.12.g1aadc9b9.dmg
Android Package (APK)	kolibri-0.17.3a0.dev0+git.12.g1aadc9b9-0.1.4-debug.apk
TAR file	kolibri-0.17.3a0.dev0+git.12.g1aadc9b9.tar.gz
WHL file	kolibri-0.17.3a0.dev0+git.12.g1aadc9b9-py2.py3-none-any.whl

[rtibbles]

I am not sure that we are properly setting psycopg2 up with unicode handling as described here? https://www.psycopg.org/docs/usage.html#unicode-handling

This might point to a way to handle this in a way that doesn't cause a huge performance regression.

Also, I think we should add a regression test for the specific case we are fixing here - a importing a unicode string for a node title that is at the max length.

[jredrejo]

Also, I think we should add a regression test for the specific case we are fixing here - a importing a unicode string for a node title that is at the max length.

Done

[rtibbles]

Just a couple of questions to make sure the tests are doing what they ought - if the answer to my second question is yes, then we might need two test cases, one with utf-8 that is short enough but would overflow if it was converted to bytes, and another where the tag is just too long regardless.

I will manually test this to compare speed before and after.

[rtibbles]

This should be good to go, once I've done the speed test locally just to verify, will do tomorrow.

[rtibbles]

Local testing shows no performance regressions with these changes.