A migrator for upgrading v1 to v2

[louislam]

Mainly for Docker users

• Change the data dir's owner to node from root

docker run --rm -v uptime-kuma:/app/data --pull always louislam/uptime-kuma:migrator

Alternatively, if users know their path, they could use:

chown -R 1000:1000 <volume or binding path>

But not everyone knows the path, so the migrator will be easier to use.

Also renamed dockerfile to Dockerfile along with this pr.

[mhkarimi1383]

@louislam

Also a migrator between SQLite and MySQL would be awesome

[louislam]

Close as the plan was changed #4052