[JENKINS-41289] use readOnlyMode to include edit-config in show-config

[mawinter69]

Setting var readOnlyMode in jelly will basically disable all inputs, buttons, selects. So in the show-config.jelly files we can just set this var and the include the edit-config. So we no longer need to double maintain the fields.
For those configs that add credentials check the readOnlyMode variable and disable the delete and add buttons accordingly

On order to view a job configuration when one has extended read but no configure it must be avoided that the permissions checks in doCheck and doFill methods check for configure only, they should also allow EXTENDED_READ.

Testing done

Interactive testing
create for each type a config, when credentials are there add and delete buttons are still there and all fields are editable
create freestyle job and add a buildwrapper to provide credentials, for each config type go to the view details link, all fields are readonly and there are no buttons to add/remove credentials.
(note that the email ext plugin provides 2 config file types but misses to provide show-config.jelly files, thus the view details link leads to broken pages, this problem existed before)

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[mawinter69]

There is one drawback to this approach, the actual file content is no longer shown with codemirror but only as plain text. That would require a change in core to have textareas with codemirror in readonly mode keep the codemirror styling