Add sponsor message in F# giraffe generator

[wing328]

Add sponsor message in F# giraffe generator

[main] INFO  o.o.codegen.TemplateManager - writing file samples/server/petstore/fsharp-giraffe/.openapi-generator/VERSION
[main] INFO  o.o.codegen.TemplateManager - writing file samples/server/petstore/fsharp-giraffe/.openapi-generator/FILES
################################################################################
# Thanks for using OpenAPI Generator.                                          #
# Please consider donation to help us maintain this project 🙏                 #
# https://opencollective.com/openapi_generator/donate                          #
#                                                                              #
# This generator's contributed by Nick Fisher (https://github.com/nmfisher)    #
# Please support his work directly via https://paypal.me/nickfisher1984 🙏     #
################################################################################

cc @nmfisher

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