Update versions in pom.xml and documentation after 1.2.1 release

[github-actions]

• Versions are updated in pom.xml, README.md and in examples
• Current project version is incremented to the next snapshot

[codecov]

Codecov Report

Merging #1418 (9d2ac17) into master (6c70495) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1418   +/-   ##
=========================================
  Coverage     83.37%   83.37%           
  Complexity     2561     2561           
=========================================
  Files           107      107           
  Lines          7604     7604           
  Branches       2100     2100           
=========================================
  Hits           6340     6340           
  Misses          374      374           
  Partials        890      890           

Flag	Coverage Δ
unittests	83.37% <ø> (ø)

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[github-actions]

JUnit Tests (macOS, EnricoMi/publish-unit-test-result-action@v1)

1 280 tests   1 265 ✔️  11m 44s ⏱️
   159 suites       15 💤
   159 files           0 ❌

Results for commit 9d2ac17.

[github-actions]

JUnit Tests (Windows, EnricoMi/publish-unit-test-result-action@v1)

1 280 tests   1 265 ✔️  7m 44s ⏱️
   159 suites       15 💤
   159 files           0 ❌

Results for commit 9d2ac17.