chore: Add instructions how to add a manuall PAT secret (#2383 -> 7.50.x)

[vinokurig]

Add instructions how to add a manuall PAT secret to be able to create factory from private repo if oAuth is not configured.

What does this pull request change?

Chery pick from the main branch, see #2383 (comment)

What issues does this pull request fix or reference?

Specify the version of the product this pull request applies to

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The author and the reviewers validate the content of this pull request with the following checklist, in addition to the automated tests.

• Any procedure:
  • Successfully tested.
• Any page or link rename:
  • The page contains a redirection for the previous URL.
  • Propagate the URL change in:
    • Dashboard default branding data
    • Chectl constants.ts
• Builds on Eclipse Che hosted by Red Hat.
• the Validate language on files added or modified step reports no vale warnings.

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[l0rd]

@vinokurig for my understanding: why we need 2 distinct procedures? I would have rather replaced the existing one (using-a-git-credentials-store_che) with the new one (using-a-git-provider-access-token_che) since the git credential store will be created automatically with the new one hiding that complexity from the user. But more importantly the using-a-git-credentials-store_che has a big problem with repositories that have a devfile in it and I would discourage it at all. If what I am saying makes sense I can create a new PR to remove the old procedure.

[vinokurig]

@l0rd I don't think that the procedureusing-a-git-credentials-store_che is redundant because even if it could be created form the PAT secret, user might want to create it separately. However I am OK to have just one approach, so you are welcome with a PR.