Issue 16 - Move policy evaluation code from iSHARE-compliant authorization mode module to separate utility module

[dwendland]

Created two new helper modules:

• ngsi.lua containing NGSI-LD related code for payload analysis to evaluate required policies
• ishare.lua containing code related to interactions according to iSHARE specification, e.g., interactions with iSHARE authorisation registry

Changed code of attribute-based authorisation mode for usage of these new helper modules.

Solves #16

This PR allows for easier extension, for instance when adding NGSI-v2 support as well or introducing other iSHARE-compliant authorisation modules, e.g. for iSHARE-compliant role-based access

[github-actions[bot]]

Please apply one of the following labels to the PR: 'patch', 'minor', 'major'.

[github-actions[bot]]

Please apply one of the following labels to the PR: 'patch', 'minor', 'major'.