Deprecation Notice: placeholder usage is going to be deprecated

[artemrys]

UCC uses Splunk UI to render the UI part of the add-on. Splunk UI decided to deprecate placeholder prop for some of the components. In UCC we are doing the same. It is recommended to use help instead.

• As of UCC v5.28.6 placeholder is still usable.
• Future releases are still going to support it in the globalConfig file, but do not render it in the UI.
• Future future releases are not going to support it in globalConfig file and users are going to see the error during the schema validation.

[vtsvetkov-splunk]

It was actually removed from UI in 5.29.0 (2023-09-22) which is breaking change - it broke UI tests. Should we adjust schema.json to disallow having the field?

affected: https://github.com/splunk/splunk-add-on-for-microsoft-365-defender/pull/366/

[artemrys]

It was actually removed from UI in 5.29.0 (2023-09-22) which is breaking change - it broke UI tests. Should we adjust schema.json to disallow having the field?

Yes, let's do this.