Fix: Docker Healthcheck is not happy during migration

[louislam]

Description

If the migration progress is too long, Docker Healthcheck could possibly restart Uptime Kuma. So we have to start a server.

Also display simple progress on the page.

Type of change

Please delete any options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

Checklist

• My code follows the style guidelines of this project
• I ran ESLint and other linters for modified files
• I have performed a self-review of my own code and tested it
• I have commented my code, particularly in hard-to-understand areas (including JSDoc for methods)
• My changes generates no new warnings
• My code needed automated testing. I have added them (this is optional task)

Screenshots (if any)