[docs] Update delegation documentation with code snippets when available

[asraa]

Description

Right now, adding a delegation is done by triggering a PR - we should link in to some example documentation of an open sourced repository that runs code for managing this.

• Add a reference to code that creates the POP, to replace the bash scripted tuf binary scripts https://github.com/sigstore/root-signing/pull/728/files#r1140250194
• Add a reference or code snippet to a workflow or script that opens a PR against root-signing with the added delegation metadata to the targets and the signed delegation targets file
  https://github.com/sigstore/root-signing/pull/728/files#r1140249150

[kommendorkapten]

As I already have the majority of this work done in another repository, I can work on this after easter, i,e ~mid April.

[asraa]

SG! No rush, just for tracking :)