Issue:
Bug: [BUG] Migration runner fails due to Just already present



### Description:

In `docker-compose.yml`, the `migration-runner` service fails if we run `docker compose up` more than once, because, the `just` installer doesn't handle the case where just is already installed.

### Solution:

Add a conditional check to run `just` installer only if `just` is not present already.

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 -->
The migration-runner service in the `docker-compose.yml` file fails during a second deployment as `just` installer raises `just already installed` error. This PR fixes that issue issue by adding a conditional statement which calls the just installer only when just command is not available.

### 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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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
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N/A

## 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)?
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Ran `docker compose up -d` twice.
<img width="476" height="491" alt="Screenshot 2025-10-08 at 3 44 53 PM" src="https://github.com/user-attachments/assets/c9de99cd-ac3a-4ab9-8c4e-5a1bb8d48d84" />


## Checklist
<!-- Put an `x` in the boxes that apply -->

- [x] I formatted the code `cargo +nightly fmt --all`
- [x] I addressed lints thrown by `cargo clippy`
- [x] I reviewed the submitted code
- [ ] I added unit tests for my changes where possible


Testing:

Ran `docker compose up -d` twice.
<img width="476" height="491" alt="Screenshot 2025-10-08 at 3 44 53 PM" src="https://github.com/user-attachments/assets/c9de99cd-ac3a-4ab9-8c4e-5a1bb8d48d84" />

Patch:
diff --git a/docker-compose.yml b/docker-compose.yml
index e16dd74466b..4e2600c8344 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -63,7 +63,9 @@ services:
       bash -c "
       apt-get update && apt-get install -y curl xz-utils &&
       curl --proto '=https' --tlsv1.2 -LsSf https://github.com/diesel-rs/diesel/releases/latest/download/diesel_cli-installer.sh | bash &&
-      curl --proto '=https' --tlsv1.2 -sSf https://just.systems/install.sh | bash -s -- --to /usr/local/bin &&
+      if ! command -v just >/dev/null 2>&1; then
+        curl --proto '=https' --tlsv1.2 -sSf https://just.systems/install.sh | bash -s -- --to /usr/local/bin
+      fi &&
       export PATH="$${PATH}:$${HOME}/.cargo/bin" &&
       just migrate"
     working_dir: /app