renaming "elastic" user to "username" in cloud setup docs

[rehanpfmr]

This pull request primarily involves changes to the authentication credentials in various configuration files and documentation. The key change is the replacement of the default username "elastic" with "username". This is reflected in the CHANGELOG-developer.asciidoc and CHANGELOG-developer.next.asciidoc files, which list this as a breaking change.

Authentication Credentials Update:

auditbeat/auditbeat.reference.yml, auditbeat/auditbeat.yml, deploy/cloudfoundry/filebeat/filebeat.yml, deploy/cloudfoundry/metricbeat/metricbeat.yml, dev-tools/packaging/files/ironbank/auditbeat/config/auditbeat.yml, filebeat/filebeat.reference.yml, filebeat/filebeat.yml: Updated the commented-out default username from "elastic" to "username" in the authentication credentials section. [1] [2] [3] [4] [5] [6] [7] [8] [9]
Documentation Update:

CHANGELOG-developer.asciidoc, CHANGELOG-developer.next.asciidoc: Documented the change in default username as a breaking change. [1] [2]
libbeat/docs/monitoring/monitoring-internal-collection.asciidoc, libbeat/docs/output-cloud.asciidoc, x-pack/functionbeat/docs/config-options-aws.asciidoc: Updated the example configuration to reflect the new default username. [1] [2] [3]

[cla-checker-service]

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[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @rehanpfmr? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit

NOTE: backport-v8.x has been added to help with the transition to the new branch 8.x.

[belimawr]

Hi @rehanpfmr, I'm trying to understand the motivation for this change, "elastic" is the default username we use in our documentation, it is also the default username used by Elasticsearch, many of our testing/automation tools as well as the username used when deploying on Elastic Cloud and using the cloud ID. I fail to see the benefit of this change.

[rehanpfmr]

@belimawr , this is in context to #29862
There was an ask for updating the elastic to username, for which i requested an PR

[mergify]

backport-8.x has been added to help with the transition to the new branch 8.x.

[belimawr]

Another thing I didn't understand is why you removed auditbeat/module/file_integrity/testdata/garble_macho_executable.

[belimawr]

Our documentation files are auto-generated based on templates, I don't see the templates modified on this PR, there are two of them:

• libbeat/_meta/config/output-elasticsearch.yml.tmpl
• libbeat/_meta/config/output-elasticsearch.reference.yml.tmpl

After editing them, you can generate all files by running make update from the root of the repo.

[rehanpfmr]

@belimawr , that helps. i will work on the above recommendation's and update PR accoringly

[belimawr]

@belimawr , this is in context to #29862 There was an ask for updating the elastic to username, for which i requested an PR

Thanks for the context! I wasn't aware of this request.

A tip for next time: put those references in the PR description.

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)