[CMAKE] upgrade cmake minimum version to 3.16

[dbarker]

Fixes #3598

Changes

• upgrade cmake min version from 3.14 to 3.16
• test against 3.16 in CI

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[netlify]

✅ Deploy Preview for opentelemetry-cpp-api-docs canceled.

Name	Link
🔨 Latest commit	2e87dd4
🔍 Latest deploy log	https://app.netlify.com/projects/opentelemetry-cpp-api-docs/deploys/68a8e9e89f24a0000836e058

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.03%. Comparing base (9d68c19) to head (2e87dd4).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3599      +/-   ##
==========================================
+ Coverage   90.02%   90.03%   +0.02%     
==========================================
  Files         220      220              
  Lines        7069     7069              
==========================================
+ Hits         6363     6364       +1     
+ Misses        706      705       -1     

see 1 file with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[marcalff]

Looks ok overall, with some questions on remaining cmake policies.

Also, please add an "important changes" entry in CHANGELOG.md.

[marcalff]

LGTM, thanks for the fix.