Expand the guidance around what you can use SPIFFE to authenticate to

[strideynet]

Imho, one of the ways in which we can encourage adoption of SPIFFE is to highlight the platforms/tools that you can use SPIFFE SVIDs to authenticate to, and, provide advice/guidance that may not exist elsewhere to aid people in implementation.

I think there's room for us to:

1. Add more tools/platforms to "Which Tools Work with SPIFFE?"
2. For each tool, create a distinct documentation page (e.g "Using SPIFFE with X") where we can link to resources relevant to setting up authentication with SPIFFE, and any high-level established advice (e.g known papercuts with using SPIFFE SVIDs)
3. For the most popular tools, we can produce more detailed step-by-step guidance.

We may also want to include tools/platforms which technically can integrate with SPIFFE even if the UX is not ideal - we can extend the compatibility grid/introduce a scoring system to help distinguish these. For example - e.g PostgreSQL supports authentication with X509 SVIDs however it cannot read the SPIFFE ID from the URI SAN and has limited authorization controls which makes integration more painful.