chore: safe guard gRPC size limits

[alexanderbez]

Description

The newly introduced configurable gRPC size limits would cause operators using the old config to treat these new values as 0, rightfully so as they do no exist in config. This requires operators to update their configs. This PR adds an extra safe guard such that if they do not update, the default values will still be used.

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[p0mvn]

LGTM. Thank you