CAMEL-19870 Camel AS2: Should accept MDN field name Disposition as case insensitive

[isakkirajan]

Description

• The third party AS2 server returning the MDN response with disposition field case insensitive which is as per the spec (https://www.ietf.org/rfc/rfc4130.txt) but camel as2 validates this field with case sensitive hence it fails.
• This fix is already applied to main branch and this PR is a backport to camel 3.21.x branch.

Target

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Tracking

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Apache Camel coding standards and style

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• I have run mvn clean install -DskipTests locally and I have committed all auto-generated changes

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[davsclaus]

We have backported this to the other branches, so you do not have to make more PRs