[sarankumar1325]

Fixes four dead links in the docs (all were returning 404):

• docs/instrumenting/writing_exporters.md: StandardExports.java and DefaultExports.java links pointed to client_java/blob/master/simpleclient_hotspot/..., which no longer exists since client_java 1.x removed the simpleclient modules from the default branch. The links now point to the same files on the simpleclient branch. That keeps the List<MetricFamilySamples> example the text describes.
• docs/visualization/perses.md: perses.dev/perses/docs/concepts/datasources → perses.dev/perses/docs/concepts/datasource/ (current Perses data source concept page).
• docs/instrumenting/exporters.md: Micrometer Prometheus registry docs moved from micrometer.io/docs/registry/prometheus to docs.micrometer.io/micrometer/reference/implementations/prometheus.html.

I checked each new URL and all of them return HTTP 200.

AI disclosure: I found these links with an AI-assisted link check, then checked each replacement by hand.

[krajorama]

nit: use non redirected link

Suggested change

	to [Perses documentation](https://perses.dev/perses/docs/concepts/datasource/).
	to [Perses documentation](https://perses.dev/docs/perses/latest/concepts/datasource/).