Node.js libraries require @opencensus/propagation-tracecontext but it is not in package.json

[aabmass]

index.js (for both knex and sequelize integration) requires util.js which requires @opencensus/propagation-tracecontext.

sqlcommenter/nodejs/sqlcommenter-nodejs/packages/sqlcommenter-knex/util.js

Line 15 in 5adcedb

const {TraceContextFormat} = require('@opencensus/propagation-tracecontext');

However, this dep is only in devDependencies atm. OpenCensus or OpenTelemetry are providers for tracestate/traceparent, so the dependency should be optional and only crash if the user passes tracestate/traceparent in their config.

Repro:

$ npm init -y
$ npm install @google-cloud/sqlcommenter-knex
$ node -i "require('@google-cloud/sqlcommenter-knex')"
internal/modules/cjs/loader.js:968
  throw err;
  ^

Error: Cannot find module '/usr/local/google/home/aaronabbott/repo/sqlcommenter/nodejs/sqlcommenter-nodejs/samples/express-opentelemetry/require('@google-cloud/sqlcommenter-knex')'
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:965:15)
    at Function.Module._load (internal/modules/cjs/loader.js:841:27)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:71:12)
    at internal/main/run_main_module.js:17:47 {
  code: 'MODULE_NOT_FOUND',
  requireStack: []
}

[aabmass]

I added the missing deps to peerDependencies in #26, so now the user knows to install these. However, they should really be optional depending on if the user is using this feature.