Rewrite the Jira-closer/fixes bot

The current fixes bot at qt/qtqa/scripts/jira/jira-bug-closer has developed a number of issues which are too difficult to rectify in the current architecture.

• The fixed-version field is rarely set correctly. Release notes for a new version contain vastly more Jira issues than a fixed-version filter in Jira shows. This bug occurs silently and it is unclear why the bot does not choose a fixed version when closing an issue.
• The commits field is updated with duplicated shas of tqtc/* shadow repositories when a change was originally merged in the corresponding public repo. This issue requires rearchitecting to implement a system of queries and checks to avoid duplication.
• After a change is closed, the commits field in Jira gets replaced instead of updated if a follow-up cherry-pick attempts to add to the commits field.
• The bot occasionally leaks file handles, presumably from git when operating on local repos.
• The bot contributes to congestion on codereview.qt-project.org when it clones or updates local repositories (code.qt.io cannot be used since access to tqtc repos is needed). This should be rectified by using rate-limited REST calls to gerrit instead of local repo clones.
• The bot may use an invalid Jira Issue Transition on projects which do not use the historical transition name "Close"

The new bot should:

• Utilize gerrit webhooks for incoming event stream data.
• Utilize gerrit/Jira queries to identify missed work
• Close issues where the corresponding change in gerrit has a commit message which includes the footer "Fixes:"
• Reliably identify the target version of a merged change in gerrit and update the "Fix Versions" field in Jira.
• Update the "commits" field of a Jira ticket with the merged commit sha of a given gerrit change.
• Intelligently truncate commits and fix version field data as necessary to fit in the Jira Max Character Limit (255) for custom fields.
• Dynamically identify valid state transitions for a given Jira Project and use the appropriate transition to close an issue.
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