Correct or add missing SONAR-netCDF4 variable attributes for AZFP

[emiliom]

• Add some missing variable attributes in "Sonar/Beam_group1" and "Platform" groups (eg, for backscatter_r, tilt_x, tilt_y)
• Fix temperature variable attributes in "Environment" group; they were being assigned as dataset (global), not variable attributes

[codecov-commenter]

Codecov Report

Merging #1023 (b4ec468) into dev (2736ee9) will decrease coverage by 2.94%.
The diff coverage is n/a.

📣 This organization is not using Codecov’s GitHub App Integration. We recommend you install it so Codecov can continue to function properly for your repositories. Learn more

@@            Coverage Diff             @@
##              dev    #1023      +/-   ##
==========================================
- Coverage   80.45%   77.51%   -2.94%     
==========================================
  Files          67       18      -49     
  Lines        6038     2869    -3169     
==========================================
- Hits         4858     2224    -2634     
+ Misses       1180      645     -535     

Flag	Coverage Δ
unittests	77.51% <ø> (-2.94%)	⬇️

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

Impacted Files	Coverage Δ
echopype/convert/set_groups_azfp.py	97.46% <ø> (ø)

... and 51 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[leewujung]

@emiliom : looks good, feel free to merge!