Added interactsh additional variables support

[Ice3man543]

Proposed changes

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)

[ehsandeep]

Crash when using -ni flag.

./nuclei -ni -t cves/ -u http://0.0.0.0:52190

panic: runtime error: slice bounds out of range [:-1]

goroutine 117 [running]:
github.com/projectdiscovery/nuclei/v2/pkg/protocols/common/interactsh.(*Client).MakePlaceholders(0x140003540e0, {0x140011503e0, 0x1, 0x1}, 0x140017f0c60)
	/Users/geekboy/Github/nuclei/v2/pkg/protocols/common/interactsh/interactsh.go:260 +0x20c
github.com/projectdiscovery/nuclei/v2/pkg/protocols/http.(*Request).executeRequest(0x14001b0c000, {0x140038061c8, 0x14}, 0x140031ff0e0, 0x140030d6ff0, 0x1, 0x14004339c58, 0x1)
	/Users/geekboy/Github/nuclei/v2/pkg/protocols/http/request.go:537 +0x1f00
github.com/projectdiscovery/nuclei/v2/pkg/protocols/http.(*Request).ExecuteWithResults.func1({0x1400022ed80, 0x85}, 0x0, 0x140030d6fc0)
	/Users/geekboy/Github/nuclei/v2/pkg/protocols/http/request.go:262 +0x31c
github.com/projectdiscovery/nuclei/v2/pkg/protocols/http.(*Request).ExecuteWithResults(0x14001b0c000, {0x140038061c8, 0x14}, 0x140030d6fc0, 0x140030d6ff0, 0x140030d7050)
	/Users/geekboy/Github/nuclei/v2/pkg/protocols/http/request.go:315 +0x280
github.com/projectdiscovery/nuclei/v2/pkg/protocols/common/executer.(*Executer).Execute(0x14001bc2080, {0x140038061c8, 0x14})
	/Users/geekboy/Github/nuclei/v2/pkg/protocols/common/executer/executer.go:68 +0x1c4
github.com/projectdiscovery/nuclei/v2/pkg/core.(*Engine).executeModelWithInput.func2.1(0x140036c5a28, 0x1400061b5b0, 0x3, 0x14000756420, 0x1400276c540, 0x14000695a48, 0x0, 0x0, {0x140038061c8, 0x14})
	/Users/geekboy/Github/nuclei/v2/pkg/core/execute.go:141 +0xd8
created by github.com/projectdiscovery/nuclei/v2/pkg/core.(*Engine).executeModelWithInput.func2
	/Users/geekboy/Github/nuclei/v2/pkg/core/execute.go:128 +0x5f0