Update venv to use a custom name and edit errors

[ThomasHepworth]

Type of PR

• BUG
• FEAT
• MAINT
• DOC

Is your Pull Request linked to an existing Issue or Pull Request?

An improved version of the following - #1086.

Give a brief description for the solution you have provided

Adds an improved version of the create_venv.sh script and updates some of our existing documentation around using this script and maintaining pyproject.toml.

To summarise, this PR adds:

• Support for naming the venv on the command line - it defaults to venv if nothing is entered.
• What I hope is a more useful error message should poetry install fail. This is still breaking on my machine for python versions > 3.8 (from memory) and is centred around complications w/ getting numpy installed.
• Further documentation pertaining to the maintenance and upkeep of poetry.

PR Checklist

• Added documentation for changes
• Added feature to example notebooks or tutorial (if appropriate)
• Added tests (if appropriate)
• Updated CHANGELOG.md (if appropriate)
• Made changes based off the latest version of Splink
• Run the linter