[ENH] Updates to langchain: version bump, observability

[paxcema]

Description

• Updated langchain version to 0.1.9 in all handlers to match other PRs that have bumped this dep, too.
• Added support for langfuse observability in langchain handler
• Change imports to langchain_community where applicable, to minimize/remove console warnings.

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)
• 📄 This change requires a documentation update (@martyna-mindsdb we should mention there is support for Langfuse)

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.

[tmichaeldb]

Love to see more observability 😍