feat: Add runtime tags to Next.js errors

[iker-barriocanal]

Add a new tag runtime on the frontend with the value browser and the backend with the value node for the Next.js SDK.

Other minor changes:

• Some errors captured by the plugin are not actual errors and contain unuseful and/or misleading data. To avoid this, only actual errors are captured as exceptions, and the others are captured as messages.
• Remove unused @sentry/minimal package.
• Remove undefined args from on-error-client in the plugin.

The tags are added to help users identify where errors are happening, from a high-level perspective (frontend, browser; or backend, node).

on-error-client, in the plugin, only captures exceptions if the error is an actual Error. Some errors are launched with missing data (for example, no stack trace), and what users see in the issue is misleading. In those cases, instead of capturing the exception itself, what's being captured (as a message) is the error message, so that it still reaches the issue list but doesn't contain random data.

[github-actions]

size-limit report

Path	Size
@sentry/browser - CDN Bundle (gzipped)	20.28 KB (+0.01% 🔺)
@sentry/browser - Webpack	21.18 KB (0%)
@sentry/react - Webpack	21.22 KB (0%)
@sentry/browser + @sentry/tracing - CDN Bundle (gzipped)	27.36 KB (+0.01% 🔺)

[rhcarvalho]

@iker-barriocanal please document (in the PR description) why are we adding the new tags -- that helps us understand how code got to be the way it is in the future.