[Docs] URL drilldown docs link to 404

[Dosant]

Kibana version: 7.10.0
Describe the bug:

We restructured drilldown docs: #82081 but docLinks code change didn't get into 7.10.0 release.

So in 7.10.0 some URL drilldown doc links are pointing to 404.

We need to update docs so that older links point to newer pages

Steps to reproduce:

This links are not working:

• https://www.elastic.co/guide/en/kibana/7.10/url-drilldown.html#trigger-picker
• https://www.elastic.co/guide/en/kibana/7.10/url-drilldown.html#templating
• https://www.elastic.co/guide/en/kibana/7.10/url-drilldown.html#variables

Expected behavior:

Links redirect somewhere to new docs structure from #82081

• https://www.elastic.co/guide/en/kibana/7.10/url-drilldown.html#trigger-picker -> https://www.elastic.co/guide/en/kibana/7.10/drilldowns.html#url-drilldown
• https://www.elastic.co/guide/en/kibana/7.10/url-drilldown.html#templating -> https://www.elastic.co/guide/en/kibana/7.10/url_templating.html
• https://www.elastic.co/guide/en/kibana/7.10/url-drilldown.html#variables -> https://www.elastic.co/guide/en/kibana/7.10/url_templating.html#variables

[elasticmachine]

Pinging @elastic/kibana-docs (Team:Docs)