Add ecs-logging URL attributes

[colleenmcginnis]

Related to https://github.com/elastic/observability-docs/issues/1393

Adds ECS logging GitHub URL attributes.

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[lcawl]

:ecs-logging-ruby-blob: {ecs-logging-ruby-repo}/blob/main

Drive by comment that if you want "main" to be branch-specific you could maybe use {branch} or put these in the version-specific files.

[colleenmcginnis]

maybe use {branch}

That's what I did initially but it didn't work locally (it was subbing 8.17).

put these in the version-specific files

We already have attributes for ECS logging in the version attribute files, but these use master because they are used in the elastic.co/guide URL attributes, but the branch name on GitHub is main. 🤔

[colleenmcginnis]

Stale.