Document how to use OTLP exporters with self-signed certificates

[xue20xi]

Fixes #6661

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: xue20xi / name: Guilin Liang (100a26c, abea74a, f33b175, 75aa70a, f99d373, 9b16b57)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.3%. Comparing base (0669ee0) to head (100a26c).
Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #6882     +/-   ##
=======================================
- Coverage   82.3%   82.3%   -0.1%     
=======================================
  Files        263     263             
  Lines      24418   24418             
=======================================
- Hits       20098   20097      -1     
- Misses      3938    3939      +1     
  Partials     382     382             

see 1 file with indirect coverage changes

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[xue20xi]

Hi @pellared ,
I just pushed a new commit to address your comments, could you review again?

[pellared]

Can we simplify the example so that it only demonstrate how to use self-signed certificates?

Suggested change

	// ExampleWithTLSCredentials demonstrates how to configure the exporter with certificates, including self-signed certificates.
	func ExampleWithTLSCredentials() {
	// Demonstrates how to configure the exporter using self-signed certificates.
	func Example_selfSignedCertificates() {

[pellared]

May comment was not only about the name and description of the example but related to the content as well. It should be simplified.

[pellared]

Is it needed if we add CA certificate to root CA pool?

[xue20xi]

Use new cert pool instead

[pellared]

Sill, do we need to set InsecureSkipVerify to false?

Is this not the only thing that is needed?

pool := x509.NewCertPool()
if !pool.AppendCertsFromPEM(data) {
	panic("failed to add CA certificate to root CA pool")
}
tlsCfg := &tls.Config{
	RootCAs:    certs,
}
creds := credentials.NewTLS(tlsCfg)