use adaptive sampling for the frequency grid in bode and nyquist plots

[baggepinnen]

This should both increase resolution of sharp features and reduce the number of plotted points at the same time

[JuliaControlBot]

This is an automated message.
Plots were compared to references. 1/11 images have changed, see differences below.
After pulling this PR, please update the reference images by creating a PR to ControlExamplePlots.jl here.

Difference	Reference Image	New Image
✔️ 0.008

[codecov]

Codecov Report

Attention: Patch coverage is 96.55172% with 3 lines in your changes missing coverage. Please review.

Project coverage is 92.54%. Comparing base (2729dd5) to head (ad2454c).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/ControlSystemsBase/src/plotting.jl	96.25%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #993      +/-   ##
==========================================
+ Coverage   92.44%   92.54%   +0.09%     
==========================================
  Files          41       41              
  Lines        5006     5072      +66     
==========================================
+ Hits         4628     4694      +66     
  Misses        378      378              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

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