docs: add ifeval for 7.10 release

[bmorelli25]

Summary

This PR fixes a documentation link that will break when 7.10 becomes the current stack version. It conditionally changes the link location of the Logs app docs based on the stack version defined in github.com/elastic/docs (here).

ifeval::["{branch}"=="7.9"]
APM to the {apm-app-ref}/xpack-logs.html[Logs app].
endif::[]
ifeval::["{branch}"!="7.9"]
APM to the {observability-guide}/monitor-logs.html[Logs app].
endif::[]

Admittedly, this isn't pretty, but it's the cleanest way to ensure this link continues to work for users who click it before and after the 7.10 release.

Tested by building locally with :branch: overridden to 7.9, 7.10, and master.

Target

This PR will need to be backported to 1.x.

Related issue

• https://github.com/elastic/observability-docs/issues/215
• Update current version for 7.10 docs#1994

Follow-ups

After the release of 7.10, I will backport a fix that removes the conditional code.

[ghost]

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• Build Cause: [Pull request #839 opened]

• Start Time: 2020-11-03T22:03:45.102+0000

• Duration: 3 min 49 sec