docs: update docs for the filter arg in community.BigQueryVectorStore

[cmenon12]

PR Description

In BigQueryVectorStore:

• Update docs for the filter arg to reflect the fact that it can be a dictionary or a string, and so that the IDE correctly displays them.
• Override the five similarity search methods to update their docs and type hints for the filter arg to reflect that fact that it can be a dictionary or a string. These overriding methods all just call the superclass methods.

In BigQueryVectorStore and BaseBigQueryVectorStore fix the indentation of the docs, so that the IDE correctly displays them.

Relevant issues

None

Type

🧹 Refactoring
📖 Documentation

Changes(optional)

Testing(optional)

Note(optional)

There should be no functional changes, only to the documentation and the type hints to reflect functionality that already exists.

[cmenon12]

Hi @lkuligin this is ready for review

[cmenon12]

@lkuligin sorry for the linter failure, I've copied in the code from the super class methods instead of calling the super class methods directly, to avoid the type issue. Please let me know if this is not a good approach.