Unify date format for release notes in CHANGELOG.md

[mike-healy]

The release titles in CHANGELOG.md reference the release date, but historically have used both YYYY-MM-DD and MM-DD-YYYY.

MM-DD or DD-MM prefixed formats can be ambiguous as different regions use each.

I'd suggest using YYYY-MM-DD for all dates in this document.

[rowleyaj]

i second this idea and think it might be worthwhile adopting the https://keepachangelog.com/en/1.0.0/ format

@BC-tymurbiedukhin what are you thoughts on this, as I know you're often the one to request changelog entries. I could add the changes to #2080 if you like?

[BC-tymurbiedukhin]

We should align all dates to latest date format, it would be great to update previous values @rowleyaj

[rowleyaj]

@BC-tymurbiedukhin any chance I can convince you to move towards YYYY-MM-DD instead? for the reasons that @mike-healy mentioned and also as mentioned on keep a changelog:

Confusing Dates
Regional date formats vary throughout the world and it's often difficult to find a human-friendly date format that feels intuitive to everyone. The advantage of dates formatted like 2017-07-17 is that they follow the order of largest to smallest units: year, month, and day. This format also doesn't overlap in ambiguous ways with other date formats, unlike some regional formats that switch the position of month and day numbers. These reasons, and the fact this date format is an ISO standard, are why it is the recommended date format for changelog entries.

I'm happy to raise a PR to update all the dates if you agree with this format

[mike-healy]

We should align all dates to latest date format, it would be great to update previous values @rowleyaj

The latest entry in the Changelog is 5.7.1 (07-09-2021)

In future (after September) it won't be clear to a lot of people if that's 7th September or 9th July.
We have to think about where BigCommerce or the author is based, compare it to other updates, try to asses the likelihood that BC write for a US or international audience, and then make an inference based on all that.

[BC-tymurbiedukhin]

I'm fine with updating date format, changes for stencil CLI have been requested, @rowleyaj should update existing changelog entries with a new PR

[mike-healy]

Thanks for changing the format. However since 6.0.0 the new updates in CHANGELOG.md seem to be back to MM-DD-YYYY format @rowleyaj @BC-tymurbiedukhin

[rowleyaj]

@mike-healy I think i've tracked this down to this line in stencil-cli https://github.com/bigcommerce/stencil-cli/blob/master/lib/release/questions.js#L109. This appears to have been changed at the start of 2020 in this PR bigcommerce/stencil-cli#553

Also switching the date format for changelog from yyyy-mm-dd to mm-dd-yyyy.

I'm not sure why this was done, perhaps @junedkazi can provide more context?