Support for custom header comment

[StefMa]

Contributes to #33
Adds support for a custom header comment.

@NayanTheSpaceGuy is this you're looking for? 🙃

You can just override headerComment like:

headerComment = """
  # SPDX-FileCopyrightText: Copyright line here
  #
  # SPDX-License-Identifier: License here
  """

Honestly, I'm not sure if this is the elegantes solution as it shouldn't be part of the templating I guess 🤔

Maybe introducing a bucket like pklGhaSettings { } or so would be better? 🤔

[NayanTheSpaceGuy]

Yes, that works correctly. pklGhaSettings { } sounds good too
Thanks!