Add 'seconds' field for custom timestamps

[elamperti]

Is your feature request related to a problem? Please describe Scrobbles with just hours and minutes are not enough in some cases.

Describe the solution you'd like It would be useful to have a field to specify the seconds in the timestamp to increase precision of scrobbles.

Additional context

• Requested by @VdoGmr4mCal#5755 in Discord
• This requires refactoring the timestamp component