docs(alloycli): --config.format add "alloy" to supported formats.

[jkroepke]

PR Description

Open the help of the alloy cli show the following line:ö

--config.format string The format of the source file. Supported formats: "otelcol", "prometheus", "promtail", "static". (default "alloy")

The helps feels bit misleading, because the default value is not part of the supported formats.

Which issue(s) this PR fixes

Notes to the Reviewer

PR Checklist

• CHANGELOG.md updated
• Documentation added
• Tests updated
• Config converters updated

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