Exp push/pull: update default to push/pull all from head rev

[dberenbaum]

Fixes #9595

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (0433565) 90.53% compared to head (641a2ee) 90.54%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9631   +/-   ##
=======================================
  Coverage   90.53%   90.54%           
=======================================
  Files         471      471           
  Lines       36060    36051    -9     
  Branches     5188     5179    -9     
=======================================
- Hits        32646    32641    -5     
- Misses       2819     2820    +1     
+ Partials      595      590    -5     

Impacted Files	Coverage Δ
dvc/commands/experiments/pull.py	92.85% <ø> (+1.94%)	⬆️
dvc/commands/experiments/push.py	63.63% <ø> (-1.37%)	⬇️
dvc/repo/experiments/pull.py	86.66% <100.00%> (ø)
dvc/repo/experiments/push.py	74.75% <100.00%> (ø)
tests/func/experiments/test_remote.py	100.00% <100.00%> (ø)
tests/unit/command/test_experiments.py	100.00% <100.00%> (ø)

... and 19 files with indirect coverage changes

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