Issue:
Bug: [FIX] add a configuration validation for workers



We don't have a validation check 
[number of workers in our config](https://github.com/juspay/hyperswitch/blob/94cd7b689758a71e13a3eaa655335e658d13afc8/crates/router/src/configs/settings.rs#L422) . But if the number of workers is zero actix straight out panics. Ref: https://docs.rs/actix-web/latest/actix_web/struct.HttpServer.html#method.workers

Pull request description:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [x] Bugfix
- [ ] New feature
- [ ] Enhancement
- [ ] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->
Added validation check on number workers


### Additional Changes

- [ ] This PR modifies the API contract
- [ ] 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
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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 it is an obvious bug or documentation fix
that will have little conversation).
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It fixes #3510 

## How did you test it?
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Nothing to test in this PR

## Checklist
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- [ ] I formatted the code `cargo +nightly fmt --all`
- [ ] I addressed lints thrown by `cargo clippy`
- [ ] I reviewed the submitted code
- [ ] I added unit tests for my changes where possible
- [ ] I added a [CHANGELOG](/CHANGELOG.md) entry if applicable


Testing:

Nothing to test in this PR

Patch:
diff --git a/crates/router/src/configs/validations.rs b/crates/router/src/configs/validations.rs
index 910ae754347..69d0274d704 100644
--- a/crates/router/src/configs/validations.rs
+++ b/crates/router/src/configs/validations.rs
@@ -68,10 +68,18 @@ impl super::settings::Locker {
 
 impl super::settings::Server {
     pub fn validate(&self) -> Result<(), ApplicationError> {
-        common_utils::fp_utils::when(self.host.is_default_or_empty(), || {
+        use common_utils::fp_utils::when;
+
+        when(self.host.is_default_or_empty(), || {
             Err(ApplicationError::InvalidConfigurationValueError(
                 "server host must not be empty".into(),
             ))
+        })?;
+
+        when(self.workers == 0, || {
+            Err(ApplicationError::InvalidConfigurationValueError(
+                "number of workers must be greater than 0".into(),
+            ))
         })
     }
 }