Align skipper OPA config for max request body size with OPA config

[Pushpalanka]

Describe the improvement
As of now Skipper OPA integration has a skipper specific configuration open-policy-agent-max-request-body-size to govern the max allowed request body parsing limit to safeguard against out of memory issues.

With 0.67.0 release of OPA, they have inbuilt this safeguard into OPA configuration using the below keys:

# Set max request size to 64 MB and max gzip size (decompressed) to be 128 MB.
server:
  decoding:
    max_length: 67108864
    gzip:
      max_length: 134217728

To avoid confusions on the limit based on the two configs, it's best to align them in the integration.

Expected behavior
The value set in open-policy-agent-max-request-body-size configuration in Skipper is passed to OPA, as understood by it's configs. This will make sure same config values are honored in both levels avoiding confusions.