fix: pgvector_store read connection_string from env

[wxiao1002]

pgvector_store not use PGVECTOR_CONNECTION_STRING from .env

Description

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How Has This Been Tested?

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Checklist:

• My code follows the style guidelines of this project
• I have already rebased the commits and make the commit message conform to the project standard.
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• Any dependent changes have been merged and published in downstream modules

[Aries-ckt]

LGTM. thanks for your contribution.

[chenliang15405]

@wxiao1002 thanks for you contributtion. please fix code format, you can run command make fmt fix it

[chenliang15405]

LGTM

[Aries-ckt]

LGTM.