Proposal of moving "StaticNTPServers" to time interface.

[Lei Yu]

This email proposes to move `StaticNTPServers` from
`EthernetInterface` to  `Time.Synchronization` interface, which makes
it a static setting to BMC instead of the network interfaces and makes
it easier for bmcweb/phosphor-network to handle this setting changes.

For details, refer to https://gerrit.openbmc.org/c/openbmc/docs/+/65819
Feel free to add comments in the above gerrit.

-- 
BRs,
Lei YU