fix(policy): unexpected response for purpose attributekey id update is done

[AnuragNagpure]

Description

When the tester provides an input value that is not supported for the specified purposes, the endpoint should generate an error.

Why

Changes for purpose key is implemented as per description along with changes in AttributeKeyId in db.

Issue

#68

Checklist

Please delete options that are not relevant.

• I have followed the contributing guidelines
• I have performed a self-review of my own code
• I have successfully tested my changes locally
• I have added tests that prove my changes work
• I have checked that new and existing tests pass locally with my changes
• I have commented my code, particularly in hard-to-understand areas
• I have added copyright and license headers, footers (for .md files) or files (for images)