Show cloud image insert action in slash command menu

[AlexAndBear]

Description

This bugfix makes the slash command menu include the cloud image insertion action.

Changes:

• Exported imageCloud from useEditorActions.
• Enabled image-cloud for slash commands.
• Added imageCloud() to the insert action group in markdown, html, and tiptap-json strategies.
• Extended unit tests to cover availability and slash-command behavior for cloud image insertion.

Related Issue

• Fixes N/A

How Has This Been Tested?

• test environment: local development environment (pnpm workspace)
• test case 1: pnpm test:unit --run packages/web-pkg/tests/unit/editor/composables/useEditorActions.spec.ts
• test case 2: pnpm test:unit --run packages/web-pkg/tests/unit/editor/strategies/markdown.spec.ts
• test case 3: pnpm test:unit --run packages/web-pkg/tests/unit/editor/strategies/html.spec.ts
• test case 4: pnpm test:unit --run packages/web-pkg/tests/unit/editor/strategies/tiptapJson.spec.ts

Types of changes

• Bugfix
• Enhancement (a change that doesn't break existing code or deployments)
• Breaking change (a modification that affects current functionality)
• Technical debt (addressing code that needs refactoring or improvements)
• Tests (adding or improving tests)
• Documentation (updates or additions to documentation)
• Maintenance (like dependency updates or tooling adjustments)