chore: leave the validation of setHeaderRoute to the plugin when plugins is not empty.

[andyliuliming]

leave the validation of setHeaderRoute to the plugin when plugins is not empty.
resolving #2899

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this is a chore.
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• I've signed my commits with DCO
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• My builds are green. Try syncing with master if they are not.
• My organization is added to USERS.md.

[github-actions]

E2E Tests Published Test Results

    4 files      4 suites   3h 48m 21s ⏱️
102 tests   83 ✔️   6 💤 13 ❌
428 runs  384 ✔️ 24 💤 20 ❌

For more details on these failures, see this check.

Results for commit 358a1e8.

♻️ This comment has been updated with latest results.

[github-actions]

Go Published Test Results

2 047 tests   2 047 ✔️  2m 40s ⏱️
   118 suites         0 💤
       1 files           0 ❌

Results for commit 358a1e8.

♻️ This comment has been updated with latest results.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
32.6% Duplication

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (20214b4) 81.73% compared to head (7aac6d4) 81.68%.

❗ Current head 7aac6d4 differs from pull request most recent head 358a1e8. Consider uploading reports for the commit 358a1e8 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2898      +/-   ##
==========================================
- Coverage   81.73%   81.68%   -0.05%     
==========================================
  Files         134      133       -1     
  Lines       20406    20309      -97     
==========================================
- Hits        16678    16589      -89     
+ Misses       2869     2862       -7     
+ Partials      859      858       -1     

Files	Coverage Δ
pkg/apis/rollouts/validation/validation.go	95.57% <100.00%> (ø)

... and 17 files with indirect coverage changes

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[zachaller]

Can you give an example of why you need this validation removed. Also, argo rollouts supports multiple traffic routers at once I am unsure if it is the right move to turn off validation if say istio and a plugin are used together.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
23.3% Duplication

[andyliuliming]

Can you give an example of why you need this validation removed. Also, argo rollouts supports multiple traffic routers at once I am unsure if it is the right move to turn off validation if say istio and a plugin are used together.

@zachaller we are trying to use the max traffic weight > 100.

so 2 ways for us:

1. use the set traffic header to do the header regex
2. add support for the max weight > 100 as I was trying to do it in this PR:
   https://github.com/argoproj/argo-rollouts/pull/2900/files#diff-d4a6b587ffdebe4f22c2cc8b65d601c03c9eb897a06f36c1f633778db3fbe58e
   but that PR is more complex than I expected, since looks like the max weight is not in the spec, so some breaking change may needed, I'm still going through the code to try to find a way to not add breaking change

this PR is to try the #1 way.

[andyliuliming]

@zachaller maybe add one field
MaxTrafficWeight *int32 json:"maxTrafficWeight,omitempty" protobuf:"varint,10,opt,name=maxTrafficWeight" into RolloutTrafficRouting struct is accepatable?

drafting PR:
#3215

I will try to do some sanity check on the usage. and add ut later.