adding no_proxy env variable by default to each clab node

[toweber]

Fix #2350

If no_proxy or NO_PROXY variable is already set, existing values are kept, missing default values (127.0.0.1, localhost,...) are added and clab mgmt nets, all clab nodenames and IPs (if available) are added.
For the clab node, both no_proxy and NO_PROXY are set to the same value

Example for https://github.com/srl-labs/srl-telemetry-lab/
no_proxy=localhost,127.0.0.1,::1,*.local,172.80.80.0/24,172.80.80.11,172.80.80.12,172.80.80.13,172.80.80.21,172.80.80.22,172.80.80.31,172.80.80.32,172.80.80.33,172.80.80.41,172.80.80.42,172.80.80.43,172.80.80.45,172.80.80.46,client1,client2,client3,gnmic,grafana,leaf1,leaf2,leaf3,loki,prometheus,promtail,spine1,spine2

[hellt]

Thanks @toweber
great work!

[codecov]

Codecov Report

Attention: Patch coverage is 73.68421% with 15 lines in your changes missing coverage. Please review.

Project coverage is 51.83%. Comparing base (0984943) to head (e2c6551).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
clab/config.go	73.68%	12 Missing and 3 partials ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #2351    +/-   ##
========================================
  Coverage   51.82%   51.83%            
========================================
  Files         172      172            
  Lines       17000    17136   +136     
========================================
+ Hits         8811     8882    +71     
- Misses       7267     7324    +57     
- Partials      922      930     +8     

Files with missing lines	Coverage Δ
clab/config.go	67.62% <73.68%> (+0.54%)	⬆️

... and 9 files with indirect coverage changes