Add lifetime damage equivalent load function

[hivanov-nrel]

Currently, a short-term damage equivalent load function exists in the loads module. However, many users will also likely be interested in calculating lifetime damage equivalent loads. This function will be heavily based on the documentation provided from Mlife software. A key point to keep in mind is implementing wave and tidal resources rather than wind.

[ssolson]

@hivanov-nrel did we implement this?

[hivanov-nrel]

@ssolson we have not completed this....it has been on the back burner for awhile. Need to revisit if something provided by WDRT would be more favorable.

[ssolson]

Thanks, @hivanov-nrel could you help me out by taking a look at the WDRT functionality (added in #141) and let me know what would be the plan to close out this issue?

[hivanov-nrel]

@ssolson I discussed this issue briefly with Rebecca today. I think we can slate it to be available for the next release on June, 2023 at the latest with the goal of completing it in the January time frame. The steps will be:

1. Assess current WDRT fatigue calculation compared to IEC standards, ease of use for users, and industry relevancy
2. Implement either WDRT fatigue method or IEC standard calculation based on Mlife software program

[ssolson]

Closing due to inactivity.