Consolidate the `docs` directory

[alexander-yevsyukov]

We need to improve the directory structure of the Documentation project. The primary reason for this is to have the common structure of the docs folder for this Documentation project and for the documentations of the libraries. The common structure would reduce the maintenance efforts and free time for writing the documentation itself.

Here is the list of the improvements we need to make and associated reasoning.

• Move _code under docs
  A library project has the main code and the code associated with the documentation.
  The latter should be treated as a part of the documentation. Hence this move request.
  It does not relate to this Documentation project but is very much important for a library docs.

• Move binary files under docs/_bin
  Currently embed-code-macos are located under the _code. This placement is misleading because these binary files are not part of the code used in the documentation. They are utilities that are needed to generate the documentation.

• Fix the placement and the name of config-v1.yml
  Now the file is placed under the _code directory.
  The name of the file should be improved to reflect the nature of the file. A preferred name would be like v1.embed-code.yml. The file could be placed along the binaries or in the docs/_settings directory.

• Move the _script directory under docs
  Now the directory is at the root of the project. Since this directory is for documentation only it should be placed under docs.

• Move the site directrory under docs and add the underscore prefix
  Since this is a working folder which does not belong to the final content it should come with the _ prefix.
  Also, the directory makes sense only in the context of the documentation. So it should be under the docs.
  The move is needed for having the common structure for the documentation of the libraries.

[alexander-yevsyukov]

This PR in Validation already has the suggested structure. So, please have a look at it so that it's clear what I'm trying to achieve.

The PR only suggest the structure. I have not made it build the docs.

A separate issue which is related to the structure is sharing the common files in accross the docs directories on the main Documentation project and documentation of the libraries. Let's keep it in mind, but fix the structure matter first.

[alexander-yevsyukov]

@armiol, for your attention, in relation to the scripts issue we've had today.

Let's discuss this issue on Monday with Julia.

[alexander-yevsyukov]

Have a look at the recommendations from ChatGPT on structuring our documentation.

[alexander-yevsyukov]

@armiol, in relation to the docs-ui recommendation, I think we need to have a separate reusable UI components in the organization SpineEventEngine. Let's copy what we need from site-commons and make it local to this org, and also make it open. This way we'd make it easier for all.