Add Lumi line to Hlt2

Adds the machinery for a Hlt2 luminosity line as well as an example line.

• A lumi summary schema is generated in config.py, using the same generation algorithm already used by Allen, and is saved to the metadata repository
• A lumi line is added to Hlt2, which selects events based on the ODIN event type flag and produces an HltLumiSummary object containing two example counters (the total energy (after zero-suppression) in the ECal and HCal)
• The HltLumiWriter is added to config.py to persist the new bank to the output

The machinery functions as expected - a LumiSummary bank with the correct source ID, encoding key and counters is inserted into the output event.

Test with LHCb!4130 (merged), Rec!3426 (closed) and MooreOnline!248 (merged)