Improve init CI/CD workflow prompt

[rmorehig]

Summary

• Replace two separate CI/CD prompts with a single select prompt
• Add explicit "skip" option for users who don't want CI/CD setup
• Split GitLab workflow into separate CI and CD files (.gitlab/tinybird-ci.yaml and .gitlab/tinybird-cd.yaml)
• Update hint messages to show actual file paths

Changes

Before (2 prompts):

1. "Which git provider are you using?" → GitHub / GitLab
2. "Create CI/CD workflows for Tinybird?" → Yes / No

After (1 prompt):

◆  Set up CI/CD workflows?
│  ○ Yes, for GitHub Actions  (Creates .github/workflows/tinybird-ci.yaml and tinybird-cd.yaml)
│  ○ Yes, for GitLab CI       (Creates .gitlab/tinybird-ci.yaml and tinybird-cd.yaml)
│  ○ No, skip for now         (You can add these later)

Test plan

• Run tinybird init and select GitHub Actions
• Run tinybird init and select GitLab CI
• Run tinybird init and select skip
• Verify correct files are created for each selection

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