agent: fix db migration for value_aggregate from 20 to 39 digits

[carlosvdr]

Migrations from the indexer-rs side are using the correct value at scalar_tap_ravs > value_aggregate since it uses unsigned 128bits numbers (39 digits) We had at first in mind 64 (therefore the 20 digits) but we need to increase this to match indexer-rs This also happens for the nonce where it is defined as 20 digits so we are specifying it in the migrations

WARNING!!!!!! do not ignore

After running this new migrations its necessary to restart TAP-AGENT