Updating PATCH /pipelines REST API Documentation to Include Optional `slug` Parameter

[123sarahj123]

Description

Implementation to expose an optional slug parameter to PATCH /pipelines

This PR is to update the REST API documentation to include the optional slug paramenter for docs/apis/rest-api/pipelines for updating properties of an existing pipeline.

A user can now update the pipeline slug name using PATCH /pipelines when they provide a slug parameter.

It is important to note that if a user updates the name of a pipeline without providing a slug parameter, a new slug will be generated for that pipeline that is derived from the updated name. If a user updates the name and forgot to add the slug parameter (because they wanted to preserve their pipeline slug) they can update the slug name in isolation.

Under "Update a pipeline" in the "Optional request body properties" table