Incorrect logic description in the HTTPHeaderName section

[bazilmarkov]

What would you like to be added:

Documentation for the HTTPHeaderName states that

If multiple entries specify equivalent header names, the first entry with an equivalent name MUST be considered for a match.

Actual behavior is that filters specifying equivalent header names are invalid, for example:

requestHeaderModifier:
  add:
    - name: my-header-name
      value: my-header-value
    - name: my-header-name
      value: my-header-value2

So, if multiple entries specify equivalent header names, the respective HTTP/GRPCRoute will fail with Duplicate value: map[string]interface {}{"name":"my-header-name"}, so I assume the documentation should be aligned with this description