[nikhilkumarpanigrahi]

Fixes #2219

This adds the Web Template Output Additional Permission 3.0 (WTO-AP-3.0) as a new
license exception. Software Freedom Conservancy publishes it, and projects like
Houdini use it as AGPL-3.0-or-later WITH WTO-AP-3.0-or-later.

Before this change, the exception was not detected at all. Source headers using it
were reported as plain agpl-3.0-plus.

Changes

• New exception license wto-ap-3.0 (is_exception: yes, category Copyleft Limited,
  same as the other AGPL-3.0 exceptions).
  The text comes from Houdini's copy of Web-Template-Output-Additional-Permission.txt.
  Conservancy's GitHub repo no longer hosts it, since they moved to
  https://k.sfconservancy.org/license-additional-permissions/
• New rules:
  • agpl-3.0-plus_with_wto-ap-3.0_1/_2: the AGPL-3.0-or-later WITH WTO-AP-3.0-or-later
    reference, and the License: ... tag form used in Houdini source headers.
    The tag rule is needed so that agpl-3.0-plus_271 (License AGPL-3.0 or later)
    does not also match part of the header and add an extra agpl-3.0-plus.
  • wto-ap-3.0_1/_2: the notice paragraphs from Houdini's LICENSE file.
  • wto-ap-3.0_3: the bare WTO-AP-3.0-or-later identifier.
• Datadriven tests in lic4, plus CHANGELOG and AUTHORS entries.

Results on real Houdini files

File	Before	After
app/models/activity.rb (and other source headers)	agpl-3.0-plus	agpl-3.0-plus WITH wto-ap-3.0
Web-Template-Output-Additional-Permission.txt	not detected	wto-ap-3.0
LICENSE	houdini-project	houdini-project (unchanged)

Open questions for reviewers

• Key name: I used wto-ap-3.0, following Conservancy's own short identifier.
  Happy to rename it, for example to follow the *-exception-to-agpl-3.0 pattern.
• "or later": WTO-AP-3.0-or-later is mapped to wto-ap-3.0, without a separate
  -plus key. Please tell me if you'd prefer a wto-ap-3.0-plus key.

Tasks

• Reviewed contribution guidelines
• PR is descriptively titled 📑 and links the original issue above 🔗
• Tests pass -- look for a green checkbox ✔️ a few minutes after opening your PR
• Commits are in uniquely-named feature branch and has no merge conflicts 📁
• Updated documentation pages (if applicable)
• Updated CHANGELOG.rst (if applicable)

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[nikhilkumarpanigrahi]

@AyanSinhaMahapatra this PR is ready for review.

The license_validate_ignorables_2 failure is not related to this PR. It fails on fsl-1.1_1.RULE and fsl-1.1_2.RULE (from #5121), which are missing ignorable_urls: https://fsl.software/FSL-1.1-ALv2.template.md. The same job also failed on #5364.

I am happy to open a separate PR to fix it.