change env var `VERTEX_AI_DATASTORE` value for langchain port

[yangm2]

This is a tracking issue related to #222.

	value of VERTEX_AI_DATASTORE
pre-#222	projects/tenantfirstaid/locations/global/collections/default_collection/dataStores/tenantfirstaid-corpora_1758844059585
after #222 merges	tenantfirstaid-corpora_1758844059585

There is a temporary hack in #222 in constants.py that transforms the old value into the new value.

TODO:

• merge Port to langchain #222
• change value in Settings -> Environments -> staging -> Environment Variables -> VERTEX_AI_DATASTORE
• change value in Settings -> Environments -> production -> Environment Variables -> VERTEX_AI_DATASTORE
• remove temporary hack in constants.py