[DOCS] Add more APM UI redirects to the Observability guide (elastic#…

…190061)

## Summary

In elastic#179981 we moved the APM UI
content to the Observability guide. When [backporting to the `8.14`
branch](elastic#190009) (which is the
`current` branch at the time I'm writing this) the docs build failed
because there are some links in the APM agent docs that are hard-coded
to go to the `current` version of the docs, and those links were not
properly redirected. When [`8.15` becomes the `current`
branch](elastic/docs#3036), I believe the docs
build will fail unless we implement the AsciiDoc redirects in this PR.

### For maintainers

- [ ] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

docs/redirects.asciidoc

@@ -507,6 +507,12 @@ Refer to {observability-guide}/apm-service-maps.html#service-maps-supported[Supp
 
 Refer to {observability-guide}/apm-service-overview.html[Service overview].
 
+[float]
+[[service-span-duration]]
+=== Span types average duration and dependencies
+
+Refer to {observability-guide}/apm-service-overview.html#service-span-duration[Service overview].
+
 [role="exclude",id="mobile-service-overview"]
 == Mobile service overview
 
@@ -598,6 +604,12 @@ Refer to {observability-guide}/apm-custom-links.html[Create custom links].
 
 Refer to {observability-guide}/apm-filters.html[Filter data].
 
+[float]
+[[environment-selector]]
+=== Service environment filter
+
+Refer to {observability-guide}/apm-filters.html#environment-selector[Filter data].
+
 [role="exclude",id="correlations"]
 == Find transaction latency and failure correlations