Bug: Feat: Ability to accept 3 values in ConnectorAuthType



Currently we support max 2 values from keys.conf / db
```rust
pub enum ConnectorAuthType {
    HeaderKey { api_key: String },
    BodyKey { api_key: String, key1: String },
}
```

I'm trying to integrate Cybersource, it requires [`http signatures`](https://developer.cybersource.com/docs/cybs/en-us/payments/developer/all/rest/payments/GenerateHeader/httpSignatureAuthentication.html#id193AL0O0BY4_id199IL0O0AY4). 

I will need 3 values
 * Merchant Id
 * Api Key
 * Api Secret
 
 With these I'm able to generate the http signature headers, like
 ```
 digest: "SHA-256=cwjLNSMNo0IFp7hbUtTNu+7KxaF9O67ydqKWMnQ7J5g="
 signature: 'keyid="5476633e-eff2-4e65-9834-58081207dd61", algorithm="HmacSHA256", headers="host (request-target) digest v-c-merchant-id", signature="djnWLdaLRh8xtWLCXxGIlavyRG4jBvB7gIzUWTKzPoQ="'
```

So I'm proposing 

```rust
pub enum ConnectorAuthType {
    HeaderKey { api_key: String },
    BodyKey { api_key: String, key1: String },
    SignatureKey { api_key: String, key1: String, api_secret: String },
}
```

@SanchithHegde @Narayanbhat166 @jarnura 

I can add the PR for it.

referring #58 
diff --git a/crates/router/src/types.rs b/crates/router/src/types.rs
index da5a6dcfbe3..06a1dbca5d5 100644
--- a/crates/router/src/types.rs
+++ b/crates/router/src/types.rs
@@ -213,8 +213,18 @@ pub struct ResponseRouterData<Flow, R, Request, Response> {
 #[derive(Debug, Clone, serde::Deserialize)]
 #[serde(tag = "auth_type")]
 pub enum ConnectorAuthType {
-    HeaderKey { api_key: String },
-    BodyKey { api_key: String, key1: String },
+    HeaderKey {
+        api_key: String,
+    },
+    BodyKey {
+        api_key: String,
+        key1: String,
+    },
+    SignatureKey {
+        api_key: String,
+        key1: String,
+        api_secret: String,
+    },
 }
 
 impl Default for ConnectorAuthType {

## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [x] New feature
- [ ] Enhancement
- [ ] Refactoring
- [ ] Dependency updates

## Description
This will allow us to accept 3 keys for a connector.
Generally Public key, Private key and the merchant id.

<!-- Describe your changes in detail -->


### Additional Changes

- [ ] This PR modifies the database schema
- [ ] This PR modifies application configuration/environment variables

<!-- 
Provide links to the files with corresponding changes.

Following are the paths where you can find config files:
1. `config`
2. `crates/router/src/configs`
3. `loadtest/config`
-->


## Motivation and Context
<!--
Why is this change required? What problem does it solve?
If it fixes an open issue, please link to the issue here.

If you don't have an issue, we'd recommend starting with one first so the PR
can focus on the implementation (unless its an obvious bug or documentation fix
that will have little conversation).
-->
Closes #69.

## How did you test it?

<!--
Did you write an integration/unit/API test to verify the code changes?
Or did you test this change manually (provide relevant screenshots)?
-->


## Checklist
<!-- Put an `x` in the boxes that apply -->

- [x] I formatted the code `cargo +nightly fmt`
- [x] I addressed lints thrown by `cargo clippy`
- [ ] I reviewed submitted code
- [ ] I added unit tests for my changes where possible
- [ ] I added a [CHANGELOG](/CHANGELOG.md) entry if applicable
