Make runner tags selection read-only for users who are neither project maintainer nor owner

Description

This issue is a result of this conversation

There is an option for on-demand scans (new/edit form) to select runner tags via dropdown.

Now it is available for every user.

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The result of this issue should be:

1. User is an owner or a maintainer
   • New scan -> User can see dropdown, load list with tags and set it for scanner
   • Edit scan -> User can see previously saved tags, load list of tags and edit it

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1. User is neither owner nor maintainer
   • New scan -> User can't see dropdown with tags at all
   • Edit scan -> User can see previously saved tags as a text entry without editing functionality

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Implementation steps

• Add flag on backend to on_demand_scans_form_data in ee/app/helpers/projects/on_demand_scans_helper.rb. Flag would say if user is either an owner or maintainer.
• Based on a flag on frontend : - if true -> show as is with dropdown - if 'false' -> show read only text field