example: FIPS mode on Linux

[pellared]

Towards #3460

Testing if it is possible to run the example in FIPS mode on Linux:

$ export OTEL_SERVICE_NAME="splunk-otel-go-example"
$ export OTEL_RESOURCE_ATTRIBUTES="deployment.environment=$(whoami)"
$ GOEXPERIMENT=boringcrypto SPLUNK_REALM=us0 SPLUNK_ACCESS_TOKEN=[REDACTED] go run .
HTTP request:
GET / HTTP/1.1
Host: localhost:8080
Accept-Encoding: gzip
Traceparent: 00-136bd7d8fc7ac8fc70b46b92d80ab781-332384ffe26b8457-01
User-Agent: Go-http-client/1.1

HTTP response:
HTTP/1.1 200 OK
Access-Control-Expose-Headers: Server-Timing
Date: Thu, 07 Nov 2024 14:12:02 GMT
Server-Timing: traceparent;desc="00-136bd7d8fc7ac8fc70b46b92d80ab781-eab31b07facf8fb6-01"
Content-Length: 0

The trace was present in o11y Cloud.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.49%. Comparing base (448e911) to head (d9b0fec).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3480   +/-   ##
=======================================
  Coverage   79.49%   79.49%           
=======================================
  Files          88       88           
  Lines        3507     3507           
=======================================
  Hits         2788     2788           
  Misses        645      645           
  Partials       74       74           

Flag	Coverage Δ
Linux	79.21% <ø> (ø)
Windows	75.24% <ø> (ø)
macOS	75.24% <ø> (ø)

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[MrAlias]

Do we need to say something about stability guarantees here?

https://go.dev/src/crypto/internal/boring/README

We have been working inside Google on a fork of Go that uses BoringCrypto (the core of BoringSSL) for various crypto primitives, in furtherance of some work related to FIPS 140. We have heard that some external users of Go would be interested in this code as well, so we have published this code here in the main Go repository behind the setting GOEXPERIMENT=boringcrypto.

Use of GOEXPERIMENT=boringcrypto outside Google is unsupported. This mode is not part of the Go 1 compatibility rules, and it may change incompatibly or break in other ways at any time.

[pellared]

I think we should indeed add a notice. Also probably that using it does not implies that something is FIPS compliant.