chore: rename x_primary_node setting to x_primary

[dmitryduev]

Description

...as it doesn't have to be a node, could be a different process on the same node. Also, it kind of just sounds better.

• I updated CHANGELOG.unreleased.md, or it's not applicable

Testing

How was this PR tested?

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 6 lines in your changes missing coverage. Please review.

Project coverage is 54.40%. Comparing base (e92352e) to head (59c1c71).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
core/internal/stream/handler.go	0.00%	0 Missing and 4 partials ⚠️
core/internal/stream/sender.go	0.00%	0 Missing and 2 partials ⚠️

❗ There is a different number of reports uploaded between BASE (e92352e) and HEAD (59c1c71). Click for more details.

HEAD has 35 uploads less than BASE

Flag	BASE (e92352e)	HEAD (59c1c71)
unit	25	17
system	27	1
func	2	1

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #9251       +/-   ##
===========================================
- Coverage   72.74%   54.40%   -18.35%     
===========================================
  Files         545      545               
  Lines       58127    58127               
===========================================
- Hits        42284    31622    -10662     
- Misses      15123    25777    +10654     
- Partials      720      728        +8     

Flag	Coverage Δ
func	20.53% <100.00%> (-16.52%)	⬇️
system	31.34% <33.33%> (-26.44%)	⬇️
unit	50.53% <33.33%> (-1.12%)	⬇️

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

Files with missing lines	Coverage Δ
core/internal/settings/settings.go	89.47% <100.00%> (-2.11%)	⬇️
wandb/sdk/wandb_settings.py	81.91% <100.00%> (-6.52%)	⬇️
core/internal/stream/sender.go	49.35% <0.00%> (-15.47%)	⬇️
core/internal/stream/handler.go	54.30% <0.00%> (-19.63%)	⬇️

... and 244 files with indirect coverage changes