[Clas12_calcom] Micromegas DAQ constants update

[Guillaume CHRISTIAENS]

Hi all,

In order to reduce Micromegas data size, we now use "sparse samples" in 
MVT. To compute a time information correctly we need this information to 
be accessible during the decoding.

Since it's an electronic feature that we didn't know before facing this 
data size issue, ccdb table was not made to hold this information. Then 
I would like to add 2 constants and thus 2 columns to the current DAQ 
table for micromegas (/daq/config/bmt). It's only a 1-row table so not 
too heavy.

I think the only ways to add columns are to delete the table and create 
a new one, or to create a duplicate table with a different name (like 
/daq/config/bmt2). Even if it's not the spirit of ccdb, I clearly prefer 
the first solution, to keep clean and clear tables, and since it's just 
adding column, retro-compatibility will be fine.

The only issue I see is if someone is decoding a file at the moment the 
table is deleted and then created again, he may have errors.

What do you think ?

Regards,

Guillaume