Update pre-requisites for Telegram bot

[hanwg]

Proposed change

Preview: https://deploy-preview-41664--home-assistant-docs.netlify.app/integrations/telegram_bot/#prerequisites

Note:
Telegram and Telegram bot integrations are separate integrations.

Context of the change:

1. In the past, the Telegram and Telegram bot integrations are dependent on each other.
   However, this is no longer the case as the Telegram bot integration can function on its own entirely since 2025.7.
2. The Telegram integration uses the legacy notify platform which has been marked for deprecation in 2025.11.
   The plan is to redirect Telegram to Telegram bot after the deprecation (2026.5).

Changes:

1. Added a warning to the Telegram integration for the deprecation. The intend is to discourage users from using an integration that has been marked for deprecation and to direct them to the Telegram bot integration. This helps the user to avoid unnecessary migrations.
2. Updated the Telegram bot integration category to Notifications to better reflect the current nature of the integration.
3. Updated the examples in the Telegram bot integration so that they use the correct actions instead of deprecated ones.

Type of change

• Spelling, grammar or other readability improvements (current branch).
• Adjusted missing or incorrect information in the current documentation (current branch).
• Added documentation for a new integration I'm adding to Home Assistant (next branch).
  • I've opened up a PR to add logos and icons in Brands repository.
• Added documentation for a new feature I'm adding to Home Assistant (next branch).
• Removed stale or deprecated documentation.

Additional information

• Link to parent pull request in the codebase:
• Link to parent pull request in the Brands repository:
• This PR fixes or closes issue: fixes #

Checklist

• This PR uses the correct branch, based on one of the following:
  • I made a change to the existing documentation and used the current branch.
  • I made a change that is related to an upcoming version of Home Assistant and used the next branch.
• The documentation follows the Home Assistant documentation standards.

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