Settle on long-term UI api design

[ryan953]

Blueprint is currently: https://github.com/getsentry/sentry/pull/70805/files

Goals to solve for:

• No special config at the sdk layer. ie: user types Sentry.init({dsn: 'foo'}) today, that should be the same tomorrow.
• Make it possible to determine if a config is used by a client/project or not, or is it safe to delete.
• Address possible multi-writer use-cases, where different actors/bots/users want to update specific fields simultaneously.
• Allow different configs for different platforms within the same project (ie: NextJS backend vs frontend)

Some of these goals bleed into the SDK config itself, but the bulk of the JS SDK interface design won't happen as part of this ticket.

Related internal tracking items:

• https://www.notion.so/sentry/Remote-Config-API-endpoints-ca1c6a2a38d3432292bba29dc83b7182
• https://www.notion.so/sentry/Remote-Config-Web-Pages-f6e44ac3dd954aadbbb9f0b999e3e244