Remove Tasklist GraphQL API

[akeller]

Description

🪦 Removing the deprecated Tasklist GraphQL API. 🪦

I think this can be separate from a specific alpha, so it can be reviewed and merged whenever (unless @tmetzke or @aleksander-dytko think differently).

Remaining items to bring this PR out of draft status:

• Redirects (to the Camunda REST API)
• Backporting (content removal only, not announcement)

@camunda/tech-writers one of you can take this over while I'm gone to get it merged.

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support.
• This is already available but undocumented and should be released within a week.
• This on a specific schedule and the assignee will coordinate a release with the DevEx team. (apply hold label or convert to draft PR)
• This is part of a scheduled alpha or minor. (apply alpha or minor label)
• There is no urgency with this change and can be released at any time.

PR Checklist

• My changes are for an already released minor and are in /versioned_docs directory.

• My changes are for the next minor and are in /docs directory (aka /next/).

• I (will) added a redirect for a renamed or deleted page to the .htaccess file.

• My changes require an Engineering review, and I've assigned the Engineering DRI or delegate.
• My changes require a technical writer review, and I've assigned @camunda/tech-writers as a reviewer.

[github-actions]

👋 🤖 🤔 Hello, @akeller! Did you make your changes in all the right places?

These files were changed only in docs/. You might want to duplicate these changes in versioned_docs/version-8.6/.

• docs/apis-tools/tasklist-api/assets/tasklist.graphqls
• docs/apis-tools/tasklist-api/directives/category.yml
• docs/apis-tools/tasklist-api/directives/deprecated.mdx
• docs/apis-tools/tasklist-api/directives/include.mdx
• docs/apis-tools/tasklist-api/directives/skip.mdx
• docs/apis-tools/tasklist-api/directives/specified-by.mdx
• docs/apis-tools/tasklist-api/enums/category.yml
• docs/apis-tools/tasklist-api/enums/sort.mdx
• docs/apis-tools/tasklist-api/enums/task-sort-fields.mdx
• docs/apis-tools/tasklist-api/enums/task-state.mdx
• docs/apis-tools/tasklist-api/generated.md
• docs/apis-tools/tasklist-api/inputs/category.yml
• docs/apis-tools/tasklist-api/inputs/date-filter-input.mdx
• docs/apis-tools/tasklist-api/inputs/task-order-by.mdx
• docs/apis-tools/tasklist-api/inputs/task-query.mdx
• docs/apis-tools/tasklist-api/inputs/variable-input.mdx
• docs/apis-tools/tasklist-api/interfaces/category.yml
• docs/apis-tools/tasklist-api/mutations/category.yml
• docs/apis-tools/tasklist-api/mutations/claim-task.mdx
• docs/apis-tools/tasklist-api/mutations/complete-task.mdx
• docs/apis-tools/tasklist-api/mutations/delete-process-instance.mdx
• docs/apis-tools/tasklist-api/mutations/unclaim-task.mdx
• docs/apis-tools/tasklist-api/objects/category.yml
• docs/apis-tools/tasklist-api/objects/form.mdx
• docs/apis-tools/tasklist-api/objects/task.mdx
• docs/apis-tools/tasklist-api/objects/user.mdx
• docs/apis-tools/tasklist-api/objects/variable.mdx
• docs/apis-tools/tasklist-api/queries/category.yml
• docs/apis-tools/tasklist-api/queries/current-user.mdx
• docs/apis-tools/tasklist-api/queries/form.mdx
• docs/apis-tools/tasklist-api/queries/task.mdx
• docs/apis-tools/tasklist-api/queries/tasks.mdx
• docs/apis-tools/tasklist-api/queries/variable.mdx
• docs/apis-tools/tasklist-api/queries/variables.mdx
• docs/apis-tools/tasklist-api/scalars/DateTime.mdx
• docs/apis-tools/tasklist-api/scalars/category.yml
• docs/apis-tools/tasklist-api/scalars/boolean.mdx
• docs/apis-tools/tasklist-api/scalars/id.mdx
• docs/apis-tools/tasklist-api/scalars/int.mdx
• docs/apis-tools/tasklist-api/scalars/string.mdx
• docs/apis-tools/tasklist-api/sidebar-schema.js
• docs/apis-tools/tasklist-api/tasklist-api-authentication.md
• docs/apis-tools/tasklist-api/tasklist-api-graphql-to-rest-migration.md
• docs/apis-tools/tasklist-api/tasklist-api-overview.md
• docs/apis-tools/tasklist-api/tasklist-api-tutorial.md
• docs/apis-tools/tasklist-api/unions/category.yml
• docs/reference/announcements.md

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