make enum values accept strings additionally

[lhein]

when trying to create a Kamelet (and probably in any other case where we have enums in a drop down box) I would like to put in a property placeholder but the drop down prevents that. I have to later on switch to the source view and add it there.

[igarashitm]

Same for boolean checkbox. Also see #494

Two options in my mind

1. Add a tiny button next to and say Use placeholder, once clicked it's turned into a text field
2. Always use editable dropdown for enum and boolean. Note that in this case boolean field is shown with text, true or false

I personally prefer No.1

[igarashitm]

Also take password field into account - #503

[lhein]

is shown with text, true or false
It could actually also be YES and NO. I think that option 2 is probably the more flexible approach.

[igarashitm]

Couldn't it end up like user input true, then it's shown as YES then they complains about it? 😆
Also in that case the free text input would be better limited to only a property placeholder

And what to do with password mask - #503?

[igarashitm]

One another thing is that once #494 is implemented, the enum field could get 2 set of dromdowns, 1 is for enum values and the other is for existing properties. Maybe switch by seeing if {{ is typed or not?