Add config option to specify `readOnly` volumes

[dsimansk]

Feature request

Per discussion at PR #1709.

Extend current --volume flag to accept config parameter readOnly=true to limit volume accessibility.

UI Example

--volume pvc:myvol:readOnly=true

/kind good-first-issue /kind feature

[rhuss]

Which options are actually possible ? Would be good to list those in this issue. If multiple Options can be provided that should be dependable via ,, like in --volume pvc:myvol:readOnly=true, anotherOption=42

[vyasgun]

/assign