Add timestamp of the commit as event register flag

[khanhtc1202]

What this PR does:

as title

Why we need it:

The user of pipectl should have a way to submit the timestamp of the commit that triggers the event (eventwatcher register feature)

Which issue(s) this PR fixes:

Follow PR #5650

Does this PR introduce a user-facing change?:

• How are users affected by this change:
• Is this breaking change:
• How to migrate (if breaking change):

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 11 lines in your changes missing coverage. Please review.

Project coverage is 25.55%. Comparing base (c52ff8c) to head (08f5bf0).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/app/pipectl/cmd/event/register.go	0.00%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5653      +/-   ##
==========================================
+ Coverage   25.54%   25.55%   +0.01%     
==========================================
  Files         477      477              
  Lines       51099    51101       +2     
==========================================
+ Hits        13054    13060       +6     
+ Misses      37040    37036       -4     
  Partials     1005     1005              

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