DSN should be project specific

[Shubhdeep12]

Steps to Reproduce

Its a very minor thing, but thought of adding an issue on this :sweat
In docs, we show the DSN of a project created by the user otherwise a dummy dsn url

Expected Result

If a user has created a next.js project(s), we should only show the nextjs project's DSN there.
for all other docs, we should show the example DSN.

Actual Result

We show the DSN and also give users flexibility to change the DSN if they want.the

Additional Info

i think showing only the relevant dsn url and also informing the user about configured project will help the end user.

[getsantry]

Assigning to @getsentry/support for routing ⏲️

[chargome]

We have added a search bar for DSNs in #11393, which should facilitate finding the right project. Also sometimes there is a need to add DSNs from projects that are based on different frameworks, this would not be possible then.