Improve lambda layer retrieval

[andreiborza]

Description

Today, there's one endpoint for fetching AWS lambda layer information from the release registry. This endpoint lumps node and python targets together and only returns information on the latest versions (of the latest majors) of each target.

This release registry information is used in the docs to populate this dropdown

Problem

With the v8 major of the sentry-javascript SDKs, we introduced a new layer for v7 published under its own name:
https://github.com/getsentry/sentry-javascript/blob/bc7dfd64961cc85405ca0d2ae91ea6545847a1de/.craft.yml#L147-L163

But, given the endpoint only returns information on the latest major, we cannot provide an ARN dropdown for users of previous majors. Instead, ARNs are hardcoded in the docs and are immediately out of date.

Solution Brainstorming

A couple of potential solutions:

• Add another layer underneath targets for each major, e.g. node/v7/latest.json, node/v8/latest.json, python/v3/latest.json and combine them all in the existing api endpoint
• Provide an endpoint to query the latest info of a given major, e.g. https://release-registry.services.sentry.io/aws-lambda-layers/node/7 for
  the latest node layer for the v7 major. SDKs have such an endpoint, e.g. https://release-registry.services.sentry.io/sdks/sentry.javascript.node/7.120.0