Update documentation for ENV Variables

[tino097]

Description

Update documentation with the full list of environment variables.

Fixes #issue_number

Type of change

• 📄 This change requires a documentation update

Verification Process

To ensure the changes are working as expected:

• Test Location: Specify the URL or path for testing.
• Verification Steps: Outline the steps or queries needed to validate the change. Include any data, configurations, or actions required to reproduce or see the new functionality.

Additional Media:

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Checklist:

• My code follows the style guidelines(PEP 8) of MindsDB.
• I have appropriately commented on my code, especially in complex areas.
• Necessary documentation updates are either made or tracked in issues.
• Relevant unit and integration tests are updated or added.

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[ZoranPandovski]

@martyna-mindsdb Can you please review this?

[martyna-mindsdb]

Hi @tino097
Thanks for your contribution.

We already have a doc page that lists environment variables -- https://docs.mindsdb.com/setup/environment-vars
Can you please add the missing ones to the existing doc page? Feel free to keep the format as:

- **Type:** String (path)
- **Description:** Sets the root storage directory for MindsDB
- **Default:** System-specific user data directory (`~/.local/share/mindsdb/var/` on Linux)
- **Example:** `MINDSDB_STORAGE_DIR=/opt/mindsdb/data`

[ZoranPandovski]

@tino097 can you please check why we need MINDSDB_RUNTIME I think that is some leftofever we need to remove from code too