Select - add readonly state to code

[thrbnhrtmnn]

Description / User Story

Readonly state of select is currently missing in code and needs to be added.

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Acceptance Criteria

• Select has a readonly state in code, which looks exactly like in design (icons, if otherwise shown, should be not displayed in readonly state)
• Update component documentation in Storybook
  • Move readonly to "States" in the props panel, give it a boolean control and the default "false"
  • Add "or readonly" in description of the states section after "disabled"
  • Add a sub-section titled "Readonly" incl. the texts defined in the Excel (currently marked red) and a simple example of the default Select, but with readonly=true and label="Readonly"
• Props Excel has been updated / comments have been resolved and props changed from red to black font color

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Background information

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[thrbnhrtmnn]

As discussed yesterday with @larserbach, @ChristianHoffmannS2 and @kathikraemer , the readonly state for the select is still something we want to provide, even though this is not part of the standard html select. We already had a somewhat working version with little effort.

As Kathis is no longer on the project, we can pick this up at a later point again.

[thrbnhrtmnn]

We decided to remove the readonly state in design, this task is not needed anymore