Enable full-text search for more stuff (like commits, issues and issue_comments)

[simonw]

Currently FTS is only enabled for repos and releases.

[simonw]

Current FTS code: https://github.com/dogsheep/github-to-sqlite/blob/e35eec4343aa560c58c1634cc228d0d46c442304/github_to_sqlite/utils.py#L136-L143

[simonw]

• commits: message
• issue_comments: body
• issues: title, body
• labels: name, description
• licenses: name
• milestones: title, description
• releases: name, body
• repos: name, description
• users: login, name (maybe company, bio)