[MRG] Prepare for v2.1 release

[scaramallion]

Preparation for v2.1 release

Tasks

• [x] Fix or feature added
• [x] Documentation and examples updated (if relevant)
• [x] Unit tests passing and coverage at 100% after adding fix/feature
• [x] Type annotations updated and passing with mypy

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (20993be) to head (979975f). Report is 8 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #939 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 28 28 Lines 8703 8707 +4 ========================================= + Hits 8703 8707 +4 ``` | [Files](https://app.codecov.io/gh/pydicom/pynetdicom/pull/939?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pydicom) | Coverage Δ | | |---|---|---| | [pynetdicom/\_version.py](https://app.codecov.io/gh/pydicom/pynetdicom/pull/939?src=pr&el=tree&filepath=pynetdicom%2F_version.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pydicom#diff-cHluZXRkaWNvbS9fdmVyc2lvbi5weQ==) | `100.00% <100.00%> (ø)` | | | [pynetdicom/presentation.py](https://app.codecov.io/gh/pydicom/pynetdicom/pull/939?src=pr&el=tree&filepath=pynetdicom%2Fpresentation.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pydicom#diff-cHluZXRkaWNvbS9wcmVzZW50YXRpb24ucHk=) | `100.00% <100.00%> (ø)` | |