Add pgvector support

[kendagriff]

Description

Adds support for pgvector, an extension essential to working with GPT4, and isn't included natively in contrib.

Reasons

I haven't been able to find an effective way to add pgvector support to CircleCI without a custom image—this PR brings pgvector support of the box. pgvector is useful for training LLMs, e.g. GPT4, adding embeddings and similarity queries to Postgres.

An embedding is a vector (list) of floating point numbers. The between two vectors measures their relatedness. Small distances suggest high relatedness and large distances suggest low relatedness.

https://platform.openai.com/docs/guides/embeddings/what-are-embeddings

NOTE: I added the installation steps for pgvector to the initial RUN as apt-get purge removes clang, which is necessary for make install.

Checklist

• I have made changes to the Dockerfile.template file only
• I have not made any manual changes to automatically generated files
• My PR follows best practices as described in the contributing guidelines
• (Optional, but recommended) My commits are signed

[kendagriff]

@ryanbourdais Any interest in this?

[kendagriff]

@JalexChen: Bumping this again to see if there's any interest.

[BrandonMathis]

I would be quite interested in seeing this merged. I've started doing a lot of work with storing vector embeddings in postgres and currently use this docker image in my CircleCI builds.

Any tips on how i can switch to an image build with the code in this PR to test it out? I currently have this in my CircleCI config file

      - image: cimg/postgres:12.15
        environment:
          POSTGRES_USER: 'user'
          POSTGRES_DB: 'test'
          POSTGRES_PASSWORD: ''