6715 improve documentation for dbt clean options

[asarraf]

What are you changing in this pull request and why?

This change is for addressing the issue: #6715

This is a copy of the previous PR -> #6716 (As I deleted my personal docs.getdbt.com project and the PR closed automatically)

It will help understand the flags for dbt clean command:

• --clean-project-files-only (default)
• --no-clean-project-files-only

Checklist:

1. Enhance the documentation for dbt clean
2. Link the above enhanced documentation in the Upgrading to v1.7 page

NOTE: Requires reviewing the change in the content.

Checklist

• I have reviewed the Content style guide so my content adheres to these guidelines.
• I have added checklist item(s) to this list for anything anything that needs to happen before this PR is merged, such as "needs technical review" or "change base branch."

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[asarraf]

@runleonarun @mirnawong1
Can you please review. Thanks

How can I do technical testing. I see some tests are failing.

[mirnawong1]

hey @asarraf , thanks for oepning this pr and adding more context to the dbt clean command. tested it on my end and this looks great and made some small tweaks here.

[mirnawong1]

live doc: https://docs.getdbt.com/reference/commands/clean#--clean-project-files-only