battery: auto-detect battery if none specified

[Zaphoood]

What type of PR is this? (check all applicable)

• Refactor
• Feature
• Bug Fix
• Optimization
• Documentation Update
• Other

Description

When no battery is specified, /sys/class/power_supply/ is scanned and the first entry is used. If no battery is found or if the present file doesn't read 1, the new formatting format-absent, which is PR introduces, is displayed.

Related Issues & Documents

Implements part of #2572

Documentation (check all applicable)

• This PR requires changes to the Wiki documentation (describe the changes)
• This PR requires changes to the documentation inside the git repo (please add them to the PR).
• Does not require documentation changes

In Module: battery the lines

; Use the following command to list batteries and adapters:
; $ ls -1 /sys/class/power_supply/
battery = BAT0
adapter = ADP1

should be changed to

; Use the following command to list batteries and adapters:
; $ ls -1 /sys/class/power_supply/
; Default: First usable battery in /sys/class/power_supply/
battery = BAT0
adapter = ADP1

In addition, the following lines should be inserted after the section for format-low

; Format used when no battery is present
; Available tags:
;   <label-absent> (default)
;format-absent = <label-absent>

[codecov]

Codecov Report

Merging #2735 (bdce01d) into master (f0dbb4c) will decrease coverage by 0.03%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #2735      +/-   ##
==========================================
- Coverage   13.56%   13.53%   -0.04%     
==========================================
  Files         152      152              
  Lines       11357    11384      +27     
==========================================
  Hits         1541     1541              
- Misses       9816     9843      +27     

Flag	Coverage Δ
unittests	13.53% <0.00%> (-0.04%)	⬇️

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

Impacted Files	Coverage Δ
include/modules/battery.hpp	0.00% <ø> (ø)
src/modules/battery.cpp	0.00% <0.00%> (ø)

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