Default execution name should be generated in flyteadmin

[wayner0628]

Tracking issue

Why are the changes needed?

• When user didn't specify execution prefix or name, flytekit should not generate execution name, but send an empty string and let flyteadmin generate

What changes were proposed in this pull request?

• When nothing is specified, set execution_name to an empty string, see the implementation here

How was this patch tested?

unit testing

Setup process

pytest ./tests/flytekit/unit/remote/test_remote.py

Screenshots

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

Related PRs

flyteorg/flyte#5637

Docs link

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 46.21%. Comparing base (69445ff) to head (9915cd3).
Report is 19 commits behind head on master.

Files	Patch %	Lines
flytekit/remote/remote.py	0.00%	2 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (69445ff) and HEAD (9915cd3). Click for more details.

HEAD has 4 uploads less than BASE

Flag	BASE (69445ff)	HEAD (9915cd3)
	6	2

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #2678       +/-   ##
===========================================
- Coverage   79.24%   46.21%   -33.03%     
===========================================
  Files         196      187        -9     
  Lines       19785    19196      -589     
  Branches     4008     2774     -1234     
===========================================
- Hits        15678     8871     -6807     
- Misses       3407     9888     +6481     
+ Partials      700      437      -263     

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