Adding PlainID integration documentation

[mottig30]

new file:   src/oss/python/integrations/providers/plainid.mdx

Overview

This documentation is included the adding of plain ID(https://www.plainid.com) integration with Langchain.

Type of change

Type:
New documentation page

Related issues/PRs

• GitHub issue:
• Feature PR:

• Linear issue:
• Slack thread:

Checklist

• [ x] I have read the contributing guidelines
• [ x] I have tested my changes locally using docs dev
• [ x] All code examples have been tested and work correctly
• [ x] I have used root relative paths for internal links
• [ x] I have updated navigation in src/docs.json if needed
• I have gotten approval from the relevant reviewers

Additional notes