Replace the fake upload preset in the upload_widget template

[TalLevAmi]

cld make upload_widget puts the user's cloud name into the code, but it wrote upload_preset: 'preset1'. Accounts do not have this preset, so the widget fails. The output looks complete, so the user does not know that they must change it.

Brief Summary of Changes

• cloudinary_cli/templates/html/upload_widget: replace 'preset1' with '<your_unsigned_upload_preset>' and add a comment that says to create an unsigned upload preset in the Cloudinary Console.
• test_cli_make_upload_widget checks for the placeholder.

What does this PR address?

• GitHub issue (Add reference - #XX)
• Refactoring
• New feature
• Bug fix
• Adds more tests

Are tests included?

• Yes
• No

Reviewer, please note:

• The CLI could create an unsigned preset or select one from the account. I did not do that, because the command must not change the account.

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I ran the full test suite before pushing the changes and all the tests pass.

Local test run: I ran the full suite on Python 3.8 with Click 8.1.8. The new tests pass, and they fail without the fix. 8 tests in test_cli_agent.py and test_cli_config_oauth.py fail with stderr not separately captured on this branch and on master too. These tests need Click 8.2, which needs Python 3.10 or later. CI must confirm the full result.

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