Update tooling and drop Python 2 / Django < 2.2

[protoroto]

Update tooling:

• github actions
• pre-commit
• towncrier / bump2version

Drop python 2 / Django < 2.2

[codecov]

Codecov Report

Merging #62 (d266d14) into develop (3084c1e) will increase coverage by 1.23%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##           develop       #62      +/-   ##
============================================
+ Coverage    98.76%   100.00%   +1.23%     
============================================
  Files            8         8              
  Lines          162       148      -14     
  Branches        16        16              
============================================
- Hits           160       148      -12     
+ Misses           2         0       -2     

Flag	Coverage Δ
unittests	100.00% <100.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
djangocms_page_sitemap/admin.py	100.00% <ø> (ø)
djangocms_page_sitemap/sitemap_urls.py	100.00% <ø> (ø)
djangocms_page_sitemap/cms_toolbars.py	100.00% <100.00%> (ø)
djangocms_page_sitemap/models.py	100.00% <100.00%> (ø)
djangocms_page_sitemap/settings.py	100.00% <100.00%> (ø)
djangocms_page_sitemap/sitemap.py	100.00% <100.00%> (ø)
...jangocms_page_sitemap/templatetags/robots_index.py	100.00% <100.00%> (ø)
djangocms_page_sitemap/utils.py	100.00% <100.00%> (+25.00%)	⬆️

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[yakky]

A couple of page-meta to replace with page-sitemap