adds scan strategy

[tarunKoyalwar]

Proposed changes

• Adds scan-strategy flag to nuclei
  • If value is host-spray all templates are iterated over each host
  • If value is template-spray all hosts are iterated over each template
  • If value is auto . [This is only a placeholder of template-spray for now] strategy should be selected based on given parameters and inputs.

Before this PR template-spray strategy was used and current default is template-spray

closes #3065

Checklist

• Pull request is created against the dev branch
• All checks passed (lint, unit/integration/regression tests etc.) with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[tarunKoyalwar]

Flag Usage

User should select strategy based on targets . Each strategy has its own cons and pros

1. When targets < 1000 . template-spray should be used . template spray type of scan is slightly faster but uses more RAM than host spray and should be used when targets < 1000 .

2. When targets > 1000 . host-spray should be used . host spray type of scan uses less RAM than template-spray and reuses connections and other small details which have major impact when targets > 1000 .

Note:

the only criteria is target count . and whatever the scan strategy is selected nuclei performance will depend on below two parameters

-bs -bulk-size : max number of hosts to scan in parallel
-c concurrency : max number of templates in parallel for 'given hosts'

whatever the scan type is -bs < -c

[tarunKoyalwar]

Integration Test fails due to code protocol and is not related to this PR

Running test cases for "code" protocol
[✘] Test "code/test.yaml" failed: incorrect number of results: 0 (actual) vs 1 (expected) 

[Mzack9999]

lgtm - I'm proposing the following follow ups and missing TODOs:

• Update docs with adds scan strategy  #3075 (comment)

Create the following follow up tickets:

• Implementing auto strategy selection
• Tune http.Transport and Network settings for single-host scan (ideally no HTTP connection should be closed if RFC-compliant)

[tarunKoyalwar]

• nuclei-docs Update PR scan strategy doc update nuclei-docs#101
• Implement auto selection of scan strategy #3076
• Tune http.Transport and Network Settings #3077

[ehsandeep]

@tarunKoyalwar useful addition 🎉

@Mzack9999 merging this PR as requested changes have been updated and fail tests are the result of another known issue in GH CI - #2969