Fixed #11709 Dates in custom fields not always stored in the correct format

[inietov]

Description

The Purchase Date field and every custom field that is of type date in the asset edit/create form admits other date formats than our recommended 'yyyy-mm-dd`. As I think the datepicker should be enough to mitigate this issue, I only add a readonly tag to the HTML input, so no manually date is admitted and we always rely on the date picker element to input dates into the system UI.

Of course that I open to discuss other possible fixes.

Fixes #11709

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Test Configuration:

• PHP version: 7.4.16
• MySQL version: 8.0.23
• Webserver version: nginx/1.19.8
• OS version: Debian 10

Checklist:

• I have read the Contributing documentation available here: https://snipe-it.readme.io/docs/contributing-overview
• I have formatted this PR according to the project guidelines: https://snipe-it.readme.io/docs/contributing-overview#pull-request-guidelines
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[snipe]

👍 Thanks!

[Clyde-Li]

Hi inietov, 'readonly' won't really fix the problem. And I'm still using API to update date info to my custom fields.
Can we have a validate check instead? Like this: Correctly determine if date string is a valid date in that format
Thanks.