Document CSP reporting

We've supported it for a long time, but it's not clear that we do.

Sentry doesn't make a very clear (IMO) distinction on what is a DSN or a "Public Key" or what a "Public Key" is. Sometimes, such as in the REST API, "security" is a type of DSN. In the OSS Sentry web GUI it shows both "Security" And "DSN" as part of "Public Key"

We need some way of letting users know how to configure CSP reports. Here's my best understanding of Sentry terms

• DSN - Entirely devoid of meaning yet used extensively. Vaguely conjures emotions of connecting Sentry SDK to a backend. Means both specifically the http://9d0f79f5e6d64f68ad99861aca35fa51@localhost:8000/206" syntax but also may refer to anything related to connecting a SDK to backend. You could say that a DSN is a type of DSN.
• Public Key - taken literally this is the hexidecimal part of the DSN - such as 2f887ef21246477a8e75434b253c4f51
• Security Header Endpoint - API Endpoint where CSP reports go.

So what do we do?

• I don't think we care a whole lot about what Sentry's proprietary, server focused documentation said.
• I don't think we care about how the Sentry API categorized things
• We do care about what public Sentry SDK says as it's reasonable a GlitchTip user would read these

therefore:

• Change our title in project settings from "DSN" to Public Keys (DSN)
• Refer to the SDK DSN as "DSN". So yes, DSN is still a type of DSN 🙄
• Add security endpoint under DSN