ENH: simple datetimes

Summary

This adds basic datetime customization to the WebUI.

• New caosdb-f-property-datetime-value css class for special handling of datetime properties.
• Customization is controlled (currently on on/off) via variable BUILD_MODULE_EXT_COSMETICS_CUSTOMDATETIME
• Also new css classes caosdb-v-property-datetime-customized and caosdb-v-property-datetime-customized-newvalue.

Focus

There was a lot of cargo-cult copy&paste, please check if it made sense:

• All the CSS classes: are they necessary?
• Does the edit-mode handling make sense?
• Does the previewReadyEvent hook make sense?

Test Environment

Start a server with the correct environment variable, then call this Python code to create a complex datetime property (this is more than what the edit mode currently can do):

rec = db.Record(id="316").retrieve()
rec.properties[1].value = "2023-01-02T12:34+0800"
rec.update()

Then open: https://localhost:10443/Entity/316

Check List for the Author

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• All automated tests pass
• Reference related issues caosdb/customers/leibniz-zmt/management#199
• Up-to-date CHANGELOG.md (or not necessary)
• Up-to-date JSON schema (or not necessary)
• Appropriate user and developer documentation (or not necessary)
  • How do I use the software? Assume "stupid" users.
  • How do I develop or debug the software? Assume novice developers.
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
• Appropriate user and developer documentation (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there specifications? Are they satisfied?

For further good practices have a look at our review guidelines.