Change license to Apache-2

[christophfroehlich]

We already have a mix of BSD-3-Clause and Apache-2 licenses in the file. I suggest changing the main LICENSE to Apache, but keep the old one, too.
There are several references online doing so, and github theoretically supports several licenses per repo: https://github.blog/open-source/open-source-license-usage-on-github-com/

btw: I also updated the maintainers in the package.xml

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 50.41%. Comparing base (e05102c) to head (e6eadf7).

Additional details and impacted files

@@             Coverage Diff              @@
##           ros2-master     #220   +/-   ##
============================================
  Coverage        50.41%   50.41%           
============================================
  Files                9        9           
  Lines              486      486           
  Branches            62       62           
============================================
  Hits               245      245           
  Misses             215      215           
  Partials            26       26           

Flag	Coverage Δ
unittests	50.41% <ø> (ø)

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[saikishor]

Thanks for the change!