Investigate server side use of SERIAL and change type to BIGSERIAL if needed

[UsualSpec]

At the moment, we use SERIAL IDs in the measurement_data relation:

autopower/server/database_schema.sql

Line 49 in 956049c

md_id SERIAL PRIMARY KEY,

Since we will constantly insert data into this table, the md_id will also increment per sample.

SERIAL is a signed 32-Bit INT and could overflow in the far future.
Depending on the sampling interval and how many devices are deployed, we could hit the maximum integer value one day. We may want to change to a BIGSERIAL instead.

As reference, see:
https://dba.stackexchange.com/questions/47591/should-i-be-concered-by-large-serial-values

[UsualSpec]

BIGSERIAL also needs more space since it's 64-bit. So it is a tradeoff.

[UsualSpec]

I believe that on the server side, we can even get rid of the md_id since we have ack_id, server_measurement_id - both not null which would serve as key. This would simplify things. The production server might need some updates on the DB since there the ack_id is currently allowed to be NULL for compatibility reasons.