Bump @slack/bolt version and make slackApp available globally

[archessmn]

This should fix the console spam of slack struggling to stay connected and also only require one slackApp to be made per instance running.

[jenkins-ystv]

Deployed a preview of this PR to https://pr-191-internal.dev.ystv.co.uk

Copilot reviewed 6 out of 16 changed files in this pull request and generated no suggestions.

Files not reviewed (10)

• package.json: Language not supported
• features/calendar/check_with_tech.ts: Evaluated as low risk
• server/index.ts: Evaluated as low risk
• features/userFeedback/index.ts: Evaluated as low risk
• features/calendar/check_with_tech_actions.ts: Evaluated as low risk
• app/(authenticated)/calendar/[eventID]/actions.ts: Evaluated as low risk
• app/(authenticated)/calendar/[eventID]/signUpSheetActions.ts: Evaluated as low risk
• lib/auth/slack/index.ts: Evaluated as low risk
• components/slack/SlackUserInfo.tsx: Evaluated as low risk
• components/slack/SlackChannelsProvider.tsx: Evaluated as low risk

Comments skipped due to low confidence (1)

lib/slack/slackApiConnection.ts:27

• The error message should indicate that a global app does not exist, as the function is supposed to create one if it doesn't. Suggested message: "createSlackApp was called but a global app does not exist".

invariant((globalThis as unknown as { slackApp: App | undefined }).slackApp, "createSlackApp was called but a global app already exists");