metric server: remove whitespace in front of config section

The leading whitespace in the first lines of the examples caused some
confusion and problems [0] because the config would not work with it.

Removing the whitespace will make it easier to copy and paste the
examples, causing less frustation and confusion.

Signed-off-by: Aaron Lauterer <a.lauterer@proxmox.com>
[0] https://forum.proxmox.com/threads/issue-setting-up-influxdb.70687