Editing Psycopg2 layer

==Background==
Postgres instance connectivity is a critical component of our current pipeline. This library however is not available by default in AWS Lambda which is quite a PITA.

==Current version==
As at August 2024, there are two psycopg layers available:<ref>Note that <code>psycopg2</code> is a legacy term that refers to major version 2 of the library. Version 3 was released in October 2021, and is called as <code>psycopg</code> instead. Unfortunately this syntax is used a bit interchangeably for historic reasons, so double check to avoid any confusion.</ref>

{| class="wikitable"
! Layer name || Psycopg version || Python runtime
|-
| psycop9 || 1.3.8 || 3.9
|-
| 20240828_psycopg2<ref>There are multiple versions - this relates to the latest version only.</ref> || 3.2 || 3.12
|}

Obviously layer <code>psycop9</code> is more or less EOL and should not be implemented in new functions.<ref>Existing functions should also be transitioned from this as soon as feasible.</ref>

Layer <code>20240828_psycopg2</code> is the most current available at the time of writing and should be used by default for any Postgres connection.

==Updating/making new layers==
For psycop specifically, but also generally, the following steps are necessary to make a functional layer for use in AWS Lambda:
# Create a new folder and navigate to it
# Create <code>requirements.txt</code> specifying anything necessary. For psycopg2: <code>echo 'psycopg2-binary' > requirements.txt</code>
# Install required library locally using the following filepath exactly: <code>pip install -r requirements.txt -t python/lib/python3.12/site-packages/ --upgrade</code>.<ref>Python version in this example should be amended depending on version available on your local machine AND the intended Lambda runtime.</ref>
## The filepath /lib/python3.12/site-packages/ is super duper important!!
# Zip up the dir you just made: <code>zip -r amazing.zip python</code>
# $$$

Above instructions/examples for linux only - no idea how to do any of this on Windows or Mac.

==TODO==
* Figure out how to catch new [https://www.psycopg.org/articles/tag/news/ psycopg releases] and upgrade layers accordingly.<ref>Probably just security or LTS releases but yeah nah.</ref>

==References==