feat(tracing): Bring back finishReason for interaction transactions

[0Calories]

There are several interaction transactions in production that have no spans at all, and we want to find out why this is the case.

This PR reintroduces finishReason from e0f9ca0 but only sets it as a tag for interaction transactions.

This is only temporary, this tag will allow us to diagnose the reason for why interaction transactions appear to be ending early, or without any data. We can remove it from the SDK once we've finished investigating.

Here's an example of one of these strange transactions:

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	20.25 KB (0%)
@sentry/browser - ES5 CDN Bundle (minified)	62.98 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.88 KB (0%)
@sentry/browser - ES6 CDN Bundle (minified)	55.89 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	20.64 KB (0%)
@sentry/browser - Webpack (minified)	67.41 KB (0%)
@sentry/react - Webpack (gzipped + minified)	20.66 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	48.66 KB (+0.23% 🔺)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	27.62 KB (+0.37% 🔺)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	25.87 KB (+0.38% 🔺)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	43.17 KB (-0.01% 🔽)
@sentry/replay - Webpack (gzipped + minified)	37.19 KB (0%)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	61.29 KB (+0.16% 🔺)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	54.37 KB (0%)