feat: add getInstanceUrl() to plugins SDK to expose Staffbase frontend domain

[maximizeIT]

Description:

Summary

Adds a new getInstanceUrl() method to the plugins-client-sdk that returns the URL of the Staffbase frontend instance hosting the plugin.

Changes

• src/lib/connection/commands.js — added instanceUrl: 'instance-url' command
• src/lib/connection/connector/postmessage.js — destructures instance from HELLO payload, stores instanceUrl
• src/lib/connection/connector/fallback-handlers.js — added getInstanceUrl() fallback using ancestorOrigins / document.referrer
• src/lib/connection/connector/fallback.js — added case action.instanceUrl
• src/lib/app.js — added getInstanceUrl() public API method
• src/main.js — exported getInstanceUrl
• docs/api.md + docs/usage.md — documented new method
• resources/index.html — added demo section
• Tests updated: app.test.js, connection.test.js, fallback.test.js.snap

Related PRs

• Frontend: Staffbase/frontend — adds instance URL to postMessage handshake: https://github.com/Staffbase/frontend/pull/17743
• Showcase: Staffbase/cc-plugins-client-sdk-showcase — displays value in DeviceInformation: https://github.com/Staffbase/cc-plugins-client-sdk-showcase/pull/1008

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING part in the readme.
• I have added tests to cover my changes.
• All new and existing tests passed.

Test plan:

[github-actions]

size-limit report 📦

Path	Size
src/main.js	6.71 KB (+1.39% 🔺)

[Ninerian]

Just one small nit.

[staffbase-actions]

🎉 This PR is included in version 3.1.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀