Tenacity based retry logic and fully async download

[mephenor]

This PR changes the following existing functionality:

• AsyncClient is now used during download where possible instead of the synchronous httpx client for download - upload path has only been adjusted where needed for consistency
• WorkpackageAccesor and Downloader now use a retry handler for some calls. Fetching download URLs and authorization is not included, but could be added in the future by making the retry handler more generic
• The multithreaded pool executor filling the download queue and associated logic has been replaced by equivalent async functionality using tasks and semaphores to ensure only a specified amount of downloads runs in parallel and the queue is only filled up to the specified amount. This removes explicit waits and should make this part of the code less finicky.
• New client config options (retry_status_codes, exponential_backoff_max) have been introduced and the maximum number of concurrent part downloads to run is now also exposed as config option
• Bump to 1.5.0

Had to change some core imports to directly import from the appropiate module due to circular dependencies... As this seems to happen again and again, I created I task to investigate that in the future.
Also might need to update some files from template, as there are some ignores in there due to targeting Python 3.9 compatibility.

[coveralls]

Pull Request Test Coverage Report for Build 10810140574

Details

• 225 of 254 (88.58%) changed or added relevant lines in 15 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.8%) to 72.779%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/ghga_connector/core/client.py	7	9	77.78%
src/ghga_connector/core/api_calls/work_package.py	28	31	90.32%
src/ghga_connector/cli.py	26	30	86.67%
src/ghga_connector/core/downloading/downloader.py	85	94	90.43%
src/ghga_connector/core/main.py	15	26	57.69%

Files with Coverage Reduction	New Missed Lines	%
src/ghga_connector/core/api_calls/well_knowns.py	1	90.91%
src/ghga_connector/core/client.py	1	84.21%

Totals
Change from base Build 10161219570:	0.8%
Covered Lines:	1024
Relevant Lines:	1407

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💛 - Coveralls

[TheByronHimes]

There are a few things that can be improved, nothing very big though.