Add Actions workflow file for collecting repository statistics

[matt-graham]

Should resolve #219

Adds Actions workflow file using github-repo-stats Action to record GitHub repository statistics in to a branch github-repo-stats on a daily schedule.

Requires creating a new access token with permissions to push commits and access repository statistics on this repository. The tutorial for action recommends using a classic personal access token with no expiry, however if possible would be good to avoid using such a token as it will provide (write / admin) access to all repositories under an account. Ideally we should instead use a fine-grained personal acccess token with access to just this repository and with only relevant needed permissions set. This will need to be set up by someone with admin permissions on astroinformatics organization. Once the token is created it will need to be added as a new repository secret with name GHRS_GITHUB_API_TOKEN.

[matt-graham]

Based on attempt to add an access token in meeting today (2024-12-11) looks like we may need to enable access via personal access tokens for astro-informatics organization first. Based on a bit of extrapolation from an organization I have admin access to this should be settable from this URL for someone with admin permissions on organization.

[matt-graham]

Fine grained access token now created (with expiry in 1 year) and added as a secret