[FLINK-30110] Enable from-timestamp log scan when timestamp-millis is configured

[SteNicholas]

When log.scan.timestamp-millis is configured and log.scan isn't configured, the log.scan should be setting to from-timestamp by default.

The brief change log

• FileStoreTableFactory#validateOptions should validate the case that log.scan.timestamp-millis is configured.

[JingsongLi]

Thanks @SteNicholas for the contribution.

Considering that this code is just a verification, there will be some ambiguity in setting the configuration.

I'm mainly worried that this code may be skipped here, and will still be read with full later.

Consider simply returning a StartupInitializer class from options, including scan mode and startup mills. If the mode is null, it returns full if startup mills are configured?

[JingsongLi]

Hi @SteNicholas Can you rebase the latest master? I think we can just set log.scan now, there is a safe validate method now.

[SteNicholas]

@JingsongLi, I have rebased the master branch and addressed above comments. PTAL.

[JingsongLi]

Looks good to me!