using pr_comment_id to simplify handling of issue comments

[trz42]

This PR is another step towards syncing bot codes used by NESSI and EESSI. It includes the following changes

• adds a function determine_issue_comment that returns an instance of IssueComment using either the number/id of such a comment or a search pattern (for example, the name of a tarball that is included in the body of the comment for which the instance shall be returned)
• uses this function when a comment to a pull request shall be updated
• also adds pr_comment_id argument to function upload_tarball and in there uses the updated update_pr_comment
• uses updated upload_tarball in function deploy_built_artefacts

[laraPPr]

looks good to me