gRPC cannot be upgraded from 1.66.2

[timraymond]

gRPC currently cannot be upgraded from 1.66.2 to newer versions, for unknown reasons. In #921, it was discovered that this causes Hubble Relay to become unable to connect to the agent pods. TLS connections are able to be established to agents correctly using certificates generated by certgen, but gRPC itself does not function.

We should investigate why this is and what changes need to happen in order to make gRPC upgradeable again.

This upgrade was reverted in #932. As part of the remediation there, gRPC was ignored in Dependabot's configuration (found in .github/dependabot.yaml). This should also be removed once this has been remediated so as to cause Dependabot to automatically upgrade gRPC again.

Acceptance Criteria

• gRPC can be upgraded from 1.66.2 to 1.67.0 (or beyond) without breaking Relay <-> Agent connectivity in TLS
• gRPC scanning has been re-enabled in Dependabot