Exclude servlet-api dependencies from avalon-framework

[ghost]

The referenced library version of servlet-api in avalon-framework
is rather old such that it interferes with some tests in the
feature/covide19-digital-green-certificates branch.

[ghost]

I am entirely uncertain of the implications of this exclusion. Maybe there is a negative influence on the package that uses the avalon-framework (I think, its the barcode4j dependency). Please make sure to not break existing functionality with this dependency exclusion!

[ghost]

Note: based on an investigation with @richard-infai

[ManuelB]

@tempuser5432 the avalon framework is mainly used for Apache FOP which is generating PDFs. we don't need it here.

[ghost]

So this may be integrated in the feature/covid19-green-digital-certificate branch without any worries? I would still prefere to not deviate from the main branch for shared files such that - at some point - the feature branch may be integrated into the main branch.

However, if you feel uncomfortable adding this change to the main branch, I will just add it to the feature branch.

[ManuelB]

@tempuser5432 feel free to add this pull request