[TT-11997] Backend logic for request_headers_rewrite

[buraksezer]

User description

See https://tyktech.atlassian.net/browse/TT-11997 for details of the request headers rewrite rules.

---

PR Type

Enhancement, Tests

---

Description

• Added tests for request headers rewrite rules in GraphQL middleware.
• Integrated request headers rewrite logic into the reverse proxy handler.
• Added RequestHeadersRewrite to ReverseProxyParams struct.
• Passed RequestHeadersRewrite to the GraphQL engine transport for both v1 and v2.
• Implemented logic to apply request headers rewrite rules in the GraphQL engine transport, covering three different rewrite scenarios.

---

Changes walkthrough 📝

	Relevant files
Tests	mw_graphql_test.go Add tests for request headers rewrite rules in GraphQL middleware. gateway/mw_graphql_test.go Added tests for request headers rewrite rules. Implemented three test cases for different rewrite scenarios. +137/-0
Enhancement	reverse_proxy.go Integrate request headers rewrite logic in reverse proxy handler. gateway/reverse_proxy.go Integrated request headers rewrite logic into the reverse proxy handler. +8/-7      engine.go Add RequestHeadersRewrite to ReverseProxyParams struct.    internal/graphengine/engine.go Added RequestHeadersRewrite to ReverseProxyParams struct. +8/-7      graphql_go_tools_v1.go Pass RequestHeadersRewrite to GraphQL engine transport (v1). internal/graphengine/graphql_go_tools_v1.go Passed RequestHeadersRewrite to the GraphQL engine transport. +1/-0      graphql_go_tools_v2.go Pass RequestHeadersRewrite to GraphQL engine transport (v2). internal/graphengine/graphql_go_tools_v2.go Passed RequestHeadersRewrite to the GraphQL engine transport. +1/-0      transport.go Implement request headers rewrite logic in GraphQL engine transport. internal/graphengine/transport.go Added logic to apply request headers rewrite rules in the GraphQL engine transport. Implemented three rewrite rules for request headers. +96/-1

---

💡 PR-Agent usage: Comment /help on the PR to get a list of all available PR-Agent tools and their descriptions