Use HiGHS solver by default and on production, include other OS solvers

[Bill-Becker]

• Change the default solver to HiGHS instead of Xpress
• Remove Xpress for production API on NREL servers
• End-of-Life for v1 and v2 of the API which relied on Xpress on NREL servers
• Increase default timeout limit to 600 seconds (10 mins), and increase the max to 1200 seconds (20 mins) to allow slower solvers enough time to solve certain scenarios
• Increased the max optimality tolerance to 0.2 (20%) as a tool to debug long solve times and narrow in on a solution with decreased tolerance (keep default at 0.001 (0.1%)

[zolanaj]

Thanks @Bill-Becker! One non-critical comment with the approval.

[zolanaj]

I see no harm in going higher for API users, like 3600 as the max - since harder problems might need more time.

[Bill-Becker]

I'd be fine with a larger timeout for local/other-server running the API, but I don't want to clog up the NREL servers with super-long running runs. That's actually the main motivation for keeping this reasonably low.

[zolanaj]

Makes sense to me! Thanks for clarifying.