feat: adding GERP conservation score to variant annotation

[DSuveges]

✨ Context

GERP conservation scores are easy to add as annotation to the variant set. We already have GERP bw file for the loftee prediction, so just one more line in the VEP command was necessary.

This PR contains:

• updated VEP schema that captures conservation.
• updated parser extract conservation score.
• updated in silico score normalisation logic to scale GERP scores between -1 to +1

[project-defiant]

interpretation