[extension/headerssetter] Extend the headers setter extension with header modification actions.

[kovrus]

Component(s)

extension/headerssetter

Is your feature request related to a problem? Please describe.

There will be cases when users would have to insert, update or drop certain headers, see the scenario
#7596 (comment) where users have to drop a specific header. The headers setter extension could be a good place where this functionality can be implemented.

Describe the solution you'd like

Introduce the following header actions in the header setter extension:

• insert: Inserts the new header if it does not exist.
• update: Updates the header value if it exists.
• upsert: Inserts a header if it does not exist and updates the header if it exists.
• delete: Deletes the header.

Configuration example:

extensions:
  headers_setter:
    headers:
      - key: <header>
        action: insert
        from_context: <value from context>
      - key: <header>
        action: upsert
        value: <static value>
      - key: <header>
        action: update
        from_context: <value from context>
      - key: <header>
        action: delete    

Describe alternatives you've considered

No response

Additional context

#7596