Support ISO Date Formats in Time Grains

[moizarafat]

Support ISO Date Formats as input String for Time Grains

Expected Behavior

Input String format can be the same as the Time Grains input format and ISO Date Format. Elide should be able to parse both. Also for Weekly Time Grain, It should auto-convert to Monday.

-->

Current Behavior

The input string has to match the format of the time grain. For Ex. Monthly Grain expects YYYY-MM etc.

[aklish]

1. Support ISO8601 "yyyy-MM-dd'T'HH:mm'Z" format and truncate to the underlying grain.
2. Validate that ISO8601 weeks start on a Monday.