Add cf-docs snippet automation workflow and scripts

[coldice]

Adds a github workflow to publish changes on snippets from the splice repo to the cf-docs repository automatically. Requires further app/secret setup, as detailed in https://github.com/canton-network/cf-docs/blob/feature/integrate-canton-snippet-automation/config/snippet-config/update-workflow-rev2.md#splice-gha-source.

Currently up for review - do not merge before app / secret setup completes.

[isegall-da]

@coldice this is going in the wrong direction unfortunately. The requirement is NOT to take snippets from splice docs into cf-docs. Splice docs are frozen and scheduled to be completely removed.
The requirement is to construct docs snippets from Splice code itself (e.g. yaml configs for helm charts), similarly to what Splice has been doing before the migration. Let's please not merge this, and discuss further before you make any more investment on automation regarding Spilce.