Add an "annualized growth rate" feature

[danielhuppmann]

Please confirm that this PR has done the following:

• Tests Added
• Documentation Added
• Name of contributors Added to AUTHORS.rst
• Description in RELEASE_NOTES.md Added

Description of PR

This PR adds a growth_rate() method to the timeseries and compute modules so it can be called as

df.compute.growth_rate({"Primary Energy|Wind": "Growth rate of Wind"})

where df is an IamDataFrame, or

pyam.timeseries.growth_rate(x)

where x is a pd.Series indexed over an (integer) time domain.

[codecov]

Codecov Report

Merging #604 (b91feff) into main (8dc1d27) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main    #604   +/-   ##
=====================================
  Coverage   94.2%   94.3%           
=====================================
  Files         52      53    +1     
  Lines       5415    5471   +56     
=====================================
+ Hits        5106    5162   +56     
  Misses       309     309           

Impacted Files	Coverage Δ
pyam/core.py	94.4% <ø> (ø)
pyam/compute.py	100.0% <100.0%> (ø)
pyam/timeseries.py	96.9% <100.0%> (+0.6%)	⬆️
tests/test_feature_growth_rate.py	100.0% <100.0%> (ø)

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