Add valid and expires dates to metadata

[ssokol]

Not at all a priority, but when you're doing the next bit of maintenance to the code, it would be great if the metadata included the date that the chart becomes valid / active, and the date that it expires. Something like:

valid|2024-10-31
expires|2024-11-28

[ssokol]

Another fixed value that would be useful to have in the metadata is the scheme. Chartmaker seems to use the TMS scheme so:

scheme|tms

[N129BZ]

Added valid date, expire date, and scheme fields to the metadata table.

[N129BZ]

P.S. - now updating the docker image.