feat: enable always online bot users

[slack-samples]

Type of change

• New feature

Summary

Enables features.bot_user.always_online for this sample app manifest and removes the obsolete settings.always_online field.

Updated manifest file:

• manifest.json

Requirements

• I have ensured the changes I am contributing align with existing patterns and have tested and linted my code
• I've read and agree to the Code of Conduct

Testing

• Parsed each changed manifest.json as valid JSON.
• Verified each changed manifest has features.bot_user.always_online === true.
• Verified each changed manifest does not have settings.always_online.

Reviewers

Please verify the sample can still be created with Slack CLI using this branch:

$ slack create -t slack-samples/bolt-python-custom-step-template --branch claw/always-online-manifests-2026-05-27

[slack-samples]

Closing this PR because the branch only contains formatting/newline/no-op manifest changes relative to the base branch, so there is no meaningful manifest update to review.