Fix the dimension field on ProjectSerializer to read_only

[k1won]

Motivation and context

In the api document, the 'dimension' attribute of the /api/projects endpoint (post,patch) should be marked as "readOnly: true" or excluded in the request body schema section. #4367

How has this been tested?

Checklist

• I submit my changes into the develop branch
• I have added a description of my changes into CHANGELOG file
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (read github docs)
• I have increased versions of npm packages if it is necessary (cvat-canvas,
  cvat-core, cvat-data and cvat-ui)

License

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  Feel free to contact the maintainers if that's a concern.
• I have updated the license header for each file (see an example below)

# Copyright (C) 2022 Intel Corporation
#
# SPDX-License-Identifier: MIT

[nmanovic]

@k1won , thanks for the contribution!