DF-20372 (pt 2): Update Streams PluginConfig checks and FeedID parsing

[austinborn]

DF-20372

Three changes are included here:

• Update logic to check contents of Streams PluginConfig to determine whether to access the Mercury server (previously it just checked PluginConfig == nil but the correct check is len(PluginConfig) == 0, see https://github.com/smartcontractkit/chainlink/pull/13888 for the original change.
• Fix potential nil pointer references for LinkFeedID and NativeFeedID since this was not properly tested in previous change.
• Update the Feed ID parsing to fetch versions for a new spec for feed IDs prefixed with 0x01 instead of 0x00.

[austinborn]

Aside from a linting error I just fixed, the remaining checks appear to be failing due to network connection issues:

Error: ../../hashicorp/go-plugin@v1.6.2-0.20240829161738-06afb6d7ae99/grpc_broker.go:21:2: github.com/oklog/run@v1.0.0: Get "https://proxy.golang.org/github.com/oklog/run/@v/v1.0.0.mod": stream error: stream ID 7; PROTOCOL_ERROR
Error: Process completed with exit code 1.

[cl-sonarqube-production[bot]]

Quality Gate passed

Issues
3 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
93.3% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube