[Playground] parse url_notebook example tag

[eantyshev]

resolves #24225
follow-up PR which uses new fields: #24425

example tag:

# beam-playground:
#   name: setting-pipeline
#   description: Setting pipeline example.
#   url_notebook: https://some-url/py-file.ipynb
#   multifile: false
#   context_line: 35

Resulting pg_examples entity has an old path field along with new ones: urlVCS(==path) and urlNotebook

Proposed update sequence:

1. backend deployed. New backend API provides all fields: link, url_vcs, and url_notebook to not break old frontend client
2. examples CD step is run. Both backend versions, old and new consume different pg_examples fields
3. frontend merged, deployed. New frontend consumes only url_vcs and url_notebook, ignores link
   Optional steps:

• path is removed from pg_examples, infrastructure merged, examples CD step applied
• link field removed from proto and marked reserved
• backend, frontend deployed

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[eantyshev]

below is a long-lasting issue with updating big number of entities in a transaction
really complicates testing

[eantyshev]

need to keep path, to not break old backend

[damccorm]

Is there an issue tracking its removal? If not, could we add one?

[eantyshev]

too much work for this PR(

[damccorm]

Same question as above - could we add an issue for this (or drop a link in this comment if one already exists)?

[alexeyinkin]

Please change the order of words to 'VCS URL' here and everywhere else. Also 'notebook URL'.

This is a better English, and also Robert Martin suggests the most important words at the end, and 'URL' is definitive among the two.

[eantyshev]

IMHO these concerns are less important than
the fact that these fields are logically related and are better be alphabetically adjacent

[eantyshev]

there's no place we use could use it

[alexeyinkin]

😱

[eantyshev]

the refactoring is needed, but it would be too much for this change

[alexeyinkin]

A good opportunity to add trailing commas in this and other affected files.

[alexeyinkin]

Can you check the Python's habits for acronyms? In Dart and many other languages the habit is to capitalize only the first letter. For instance the class for URI is named Uri in Dart. I guess urlVcs would better in this case.

And also since we change to 'VCS URL' order this becomes vcsUrl and notebookUrl.

[eantyshev]

this casing is already used in other Datastore fields in Playground

[github-actions]

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[damccorm]

LGTM, just had some minor nits

[damccorm]

Is there an issue tracking its removal? If not, could we add one?

[damccorm]

Same question as above - could we add an issue for this (or drop a link in this comment if one already exists)?

[eantyshev]

tasks to address the comments:
#24654
#24645

[damccorm]

Thanks!