docs(python): Update concatenation page to include relaxed and changes to rechunk

[braaannigan]

Update concatenation docs to include relaxed and changes to rechunk default behaviour

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.33%. Comparing base (2398b47) to head (028c772).
Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16775      +/-   ##
==========================================
+ Coverage   81.32%   81.33%   +0.01%     
==========================================
  Files        1424     1424              
  Lines      187215   187176      -39     
  Branches     2726     2701      -25     
==========================================
- Hits       152250   152239      -11     
+ Misses      34468    34441      -27     
+ Partials      497      496       -1     

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

[braaannigan]

Closes #15707

[braaannigan]

@stinodego Just saw that the issue also noted that align isn't documented, I'll have a look at that as well

[braaannigan]

@stinodego align added now