[Change Proposal] Add docs_structure_enforced flag in _dev/build/build.yml

[haetamoudi]

Ad part of the docs improvement project, we have created a new README structure template to be used for integrations.

To ensure consistency, we want to verify that new integration READMEs follow this structure.

Scope:
This validation will apply only to new integrations for now. Existing integrations will be updated gradually.

To avoid breaking existing integrations, the validation will only be enforced for selected ones. This will be controlled via a flag in the _dev/build/build.yml file.

The flag is named: docs_structure_enforced

Default value: false

[jsoriano]

To ensure consistency, we want to verify that new integration READMEs follow this structure.

How can we ensure that the READMEs follow a given structure?

[haetamoudi]

@jsoriano the idea is to validate the section titles are present. We don't want to validate the content.

The section titles are coming from the template created by the docs team https://docs.google.com/document/d/1T05yEE_HJQN_9n5kMkoMZ9L00Msh1ribVoH50Z15pjg/edit?tab=t.0#heading=h.tzrqef91x5gk

Here is a draft PR on the changes on elastic-package elastic/elastic-package#2716.
Here is the validation part