simplify adding metadata to vectordb

[dusvyat]

Description

simplify insert with vectordb, extra columns which aren't in schema will be assumed to be part of metadata

e.g.

insert into my_vectordb(
select 
  id, 
  body as content,  
  /* all other columns go to metadata */ 
    mail_id, to_field, from_field, subject, subject, datetime
from email_datasource.emails)

Fixes #issue_number

Type of change

(Please delete options that are not relevant)

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ⚡ New feature (non-breaking change which adds functionality)
• 📢 Breaking change (fix or feature that would cause existing functionality not to work as expected)
• 📄 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:

• I have attached a brief loom video or screenshots showcasing the new functionality or change.

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.