Adds method getDataAsJson to Attachment data and therefore also to Attachment.data
This return the attachmnt data as JSON if .json or .base64 are present in attachmentdata.
Otherwise it throws an error.

Co-authored-by: annelein <anneleinvanreijen@gmail.com>

Signed-off-by: morrieinmaas <moritz@animo.id>

fixed fct declaration and henceforth tests

Co-authored-by: annelein <anneleinvanreijen@gmail.com>

Signed-off-by: morrieinmaas <moritz@animo.id>

Signed-off-by: annelein <anneleinvanreijen@gmail.com>

Better typing/function signatures

Co-authored-by: annelein <anneleinvanreijen@gmail.com>

Signed-off-by: morrieinmaas <moritz@animo.id>

Merge branch 'feat/generic-attachment-handler' of github.com:morrieinmaas/aries-framework-javascript into feat/generic-attachment-handler

Signed-off-by: morrieinmaas <moritz@animo.id>