Allow specifying blob contents when using -addUnauthenticatedBlob

[tyilo]

Instead of just adding the blob ---BEGIN_BLOB---...---END_BLOB--- which can then be replaced with another script, I think it would be more useful if we could specify the contents of the blob.

Something like

$ echo foo > blob.txt
$ osslsigncode add -addUnauthenticatedBlob blob.txt -in foo.exe -out foo-blob.exe

[mtrojnar]

Would you submit a PR?

[tyilo]

Would you submit a PR?

I'm going on vacation so it might be a while, but after that sure.

Do you think it is ok to make -addUnauthenticatedBlob require a path?

[mtrojnar]

Do you think it is ok to make -addUnauthenticatedBlob require a path?

Your PR should not break any existing scripts that invoke osslsigncode, so -addUnauthenticatedBlob should not require a path.

[mtrojnar]

Reimplemented in #404