Add security warning to Ingest docs with dummy links

[vishaangelova]

This is a sub-issue of #1734, and the aim is to address the possibility of malicious dummy links in docs by reviewing the related Ingest docs, and adding a warning where necessary.

Parent issue description

For security reasons, we plan to replace any placeholder/fake URLs with non-hostable placeholder segments.

Remove segments that make a valid URL, including prefixes (http://) and TLDs (.com).

before:

<script src="https://<your-cdn-host>.com/path/to/elastic-apm-rum.umd.min-<version>.js" crossorigin></script>

after:

<script src="<your-url>/elastic-apm-rum.umd.min-<version>.js" crossorigin></script>

The placeholder <> can be adapted to use descriptive text for its purpose. For example, a placeholder for a splunk server might look like this:

server: <your-splunk-server-url>/<path>

Repos

Status	Repo	Markdown	AsciiDoc (8.19 only)
❌	apm-server	–	–
❌	apm-agent-android	–	–
✅	apm-agent-dotnet	#2647	–
❌	apm-agent-go	–	–
❌	apm-agent-ios	–	–
❌	apm-agent-java	–	–
❌	apm-agent-nodejs	–	–
✅	apm-agent-php	#1345	–
✅	apm-agent-python	#2407	–
❌	apm-agent-ruby	–	–
❌	apm-agent-rum-js	–	–
❌	apm-aws-lambda	–	–
✅	apm-k8s-attacher	#164	–
✅	beats	#46301	#46303 #46557
❌	ecs	–	–
❌	ecs-dotnet	–	–
❌	ecs-logging-go-logrus	–	–
❌	ecs-logging-go-zap	–	–
❌	ecs-logging-go-zerolog	–	–
❌	ecs-logging-java	–	–
❌	ecs-logging-nodejs	–	–
❌	ecs-logging-php	–	–
❌	ecs-logging-python	–	–
❌	ecs-logging-ruby	–	–
❌	ecs-logging	–	–
❌	elastic-otel-dotnet	–	–
❌	elastic-otel-java	–	–
❌	elastic-otel-node	–	–
❌	elastic-otel-php	–	–
❌	elastic-otel-python	–	–
❌	elastic-serverless-forwarder	–	–
✅	integration-docs	#892	–
❌	integrations	–	–
✅	logstash	#18070	#18194
✅	logstash-docs-md	–	#71
❌	opentelemetry	–	–
❌	ingest-docs	–	–
✅	observability-docs	–	#4957

[shainaraskas]

looking into alternatives in the parent issue

[shainaraskas]

ready