Fix OpenTelemetryService initialisation code

[pkukielka]

Changes

1. Fixing problem with externalAuthRefreshChanges not having initial value which was blocking the configuration
2. Making caching checks more correct

I discovered one problem though.

Restarting trace exported does not really work.
It always throw an error:

"OTLPExporterError: Unprocessable Entity
\tat IncomingMessage.<anonymous> (/Users/pkukielka/Work/sourcegraph/cody2/vscode/dist/extension.node.js:183479:31)
\tat IncomingMessage.emit (node:events:530:35)
\tat IncomingMessage.emit (node:domain:489:12)
\tat endReadableNT (node:internal/streams/readable:1698:12)
\tat process.processTicksAndRejections (node:internal/process/task_queues:82:21)"

We catch this error and re-initialisation seems to be passing, but then CodyTraceExporter::export is never called after that.

Test plan

Tested with debugger by:

1. Adding "cody.experimental.tracing": true to the config
2. Starting VSC
3. Asking a chat question
4. Making sure CodyTraceExporter::export was executed

Then

1. Setting cody.experimental.tracing to false
2. Restarting VSC
3. Asking a chat question
4. Making sure CodyTraceExporter::export was NOT executed