Cost explorer

[Azanul]

Problem

#811

Solution

Fixed the period filter for "Last 6 months" to exclude this month and added a new period filter for "This month" in cost explorer.

Changes Made

• Added a date helper function for getting first day of this month.
• Added the UI option for selecting "This month" period & subsequent changes to support that option.

How to Test

• Try cost explorer with "This month" period, it'll show data for only this month.
• Try cost explorer with "Last 6 months" period, it won't include this month's data anymore.

Screenshots

Notes

• Fixes Cost explorer requested date ranges are wrong #811
• I considered adding date pickers or date range widget but skipped it now for the lack of a design.

Checklist

• Code follows the contributing guidelines
• Changes have been thoroughly tested
• Documentation has been updated, if necessary
• Any dependencies have been added to the project, if necessary

Reviewers

@mlabouardy
@naisayer

[Kolawole99]

LGTM

[mlabouardy]

Thanks a million for the fix @Azanul