fix: Create the /api-docs alias when a recipe installs the module

Problem/Motivation

/api-docs answers 404. webapi_install() returns early in configuration syncing mode, which is how a recipe installs a module, so the path alias to the API documentation is never created. The README promises /api-docs.

Steps to reproduce

1. Build a site from a recipe that applies modules/contrib/webapi/recipes/default.
2. Open /api-docs as an administrator: 404.

Proposed resolution

Add the alias in every install mode, and in an update hook for sites that miss it.

Remaining tasks

• ✅ File an issue about this project
• ✅ Addition/Change/Update/Fix to this project
• ✅ Testing to ensure no regression
• ➖ Automated unit/functional testing coverage
• ➖ Developer Documentation support on feature change/addition
• ➖ User Guide Documentation support on feature change/addition
• ➖ UX/UI designer responsibilities
• ➖ Accessibility and Readability
• ❌ Reviewed by a human
• ❌ Code review by maintainers
• ❌ Full testing and approval
• ❌ Credit contributors
• ❌ Review with the product owner
• ❌ Update Release Notes
• ❌ Release

User interface changes

• N/A

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• fix: Create the /api-docs alias when a recipe installs the module

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