Bug: docs(analytics): Instructions to set up `currency_conversion` (third party dependency API)



## Requirements
After the changes by [this](#6418) PR, we need to update the documentation for `analytics` crate setup process.

## Reason
Due to the third party dependency on `currency_conversion` crate, we need to ensure the proper setup of this service as well.
diff --git a/crates/analytics/docs/README.md b/crates/analytics/docs/README.md
index 96218fc231c..eb5c26a6ba3 100644
--- a/crates/analytics/docs/README.md
+++ b/crates/analytics/docs/README.md
@@ -91,6 +91,44 @@ source = "kafka"
 
 After making this change, save the file and restart your application for the changes to take effect.
 
+## Setting up Forex APIs
+
+To use Forex services, you need to sign up and get your API keys from the following providers:
+
+1. Primary Service 
+   - Sign up for a free account and get your Primary API key [here](https://openexchangerates.org/).
+   - It will be in dashboard, labeled as `app_id`.
+
+2. Fallback Service
+   - Sign up for a free account and get your Fallback API key [here](https://apilayer.com/marketplace/exchangerate_host-api).
+   - It will be in dashboard, labeled as `access key`.
+
+### Configuring Forex APIs
+
+To configure the Forex APIs, update the `config/development.toml` or `config/docker_compose.toml` file with your API keys:
+
+```toml
+[forex_api]
+api_key = "YOUR API KEY HERE" # Replace the placeholder with your Primary API Key
+fallback_api_key = "YOUR API KEY HERE" # Replace the placeholder with your Fallback API Key 
+```
+### Important Note
+```bash
+ERROR router::services::api: error: {"error":{"type":"api","message":"Failed to fetch currency exchange rate","code":"HE_00"}}
+│
+├─▶ Failed to fetch currency exchange rate
+│
+╰─▶ Could not acquire the lock for cache entry
+```
+
+_If you get the above error after setting up, simply remove the `redis` key `"{forex_cache}_lock"` by running this in shell_
+
+```bash
+redis-cli del "{forex_cache}_lock"
+```
+
+After making these changes, save the file and restart your application for the changes to take effect.
+
 ## Enabling Data Features in Dashboard
 
 To check the data features in the dashboard, you need to enable them in the `config/dashboard.toml` configuration file.

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

- [ ] Bugfix
- [ ] New feature
- [ ] Enhancement
- [ ] Refactoring
- [ ] Dependency updates
- [x] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->
Now that `analytics` depends on `currency_conversion` crate after this [PR](#6418), we need to include instructions in `analytics` documentation to set up this service.
## Fixes #6513 
### Additional Changes

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

<!--
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1. `config`
2. `crates/router/src/configs`
3. `loadtest/config`
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## Motivation and Context
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Why is this change required? What problem does it solve?
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This is related to the PR #6418 and documents the necessary prerequisite setup info.

## How did you test it?
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## Checklist
<!-- Put an `x` in the boxes that apply -->

- [ ] 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
