feat(serverlesss): allow disabling transaction traces

[aldenquimby]

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Background

• My team runs Express inside Lambda - we have a monolithic Lambda function with express handling routing, middleware, etc
• We are using @sentry/node today, and tried adding @sentry/serverless for it's timeout warning, auto-handling of flush, and links to cloudwatch logs
• But this caused all of our performance transaction traces to have an incorrect name (and various other tag + context issues)

Proposal

• A new startTransaction boolean flag that turns on/off the transaction tracing feature of @sentry/serverless
• This will allow our team to use @sentry/serverless, but still rely on express tracingHandler for performance traces
• This also follows the general approach of the serverless package, where each feature is gated by a wrapOptions flag

Alternatives

• We tried various ways to have the express transaction name override the Lambda one, but couldn't get that working
• If there is a way to do that without needing a PR like this, that would be great!

For reviewers

• I'd recommend hiding whitespace when reviewing

[AbhiPrasad]

Thanks a lot @aldenquimby - appreciate the PR!

Release either comes out tomorrow or on Monday - let's see how CI feels 😭

[AbhiPrasad]

Released with https://github.com/getsentry/sentry-javascript/releases/tag/7.74.0!