Axios dependency contains known security vulnerabilities (GHSA-43fc-jf86-j433, GHSA-3p68-rc4w-qgx5, GHSA-fvcv-3m26-pcqx)

### Describe the bug

The current axios dependency (`^1.12.2`, resolved to `1.12.2`) contains three known security vulnerabilities:

| Advisory | Severity | Description |
|---|---|---|
| [GHSA-43fc-jf86-j433](https://github.com/advisories/GHSA-43fc-jf86-j433) | High (CVSS 7.5) | Denial of Service via `__proto__` key in `mergeConfig` — affects `>=1.0.0 <=1.13.4` |
| [GHSA-3p68-rc4w-qgx5](https://github.com/advisories/GHSA-3p68-rc4w-qgx5) | Moderate (CVSS 4.8) | `NO_PROXY` hostname normalization bypass leading to SSRF — affects `>=1.0.0 <1.15.0` |
| [GHSA-fvcv-3m26-pcqx](https://github.com/advisories/GHSA-fvcv-3m26-pcqx) | Moderate (CVSS 4.8) | Unrestricted cloud metadata exfiltration via header injection chain — affects `>=1.0.0 <1.15.0` |

Since `aws-crt-nodejs` is a transitive dependency of `aws-sdk` and `aws-sdk-v3`, these vulnerabilities are inherited by all downstream consumers. This is also related to #607.

### Regression Issue

- [ ] Select this option if this issue appears to be a regression.

### Expected Behavior

The `axios` dependency should be pinned to a version that has no known security vulnerabilities (`>=1.15.1`).

### Current Behavior

Running `npm audit` on a project that depends on `aws-crt-nodejs` reports:

```
axios >=1.0.0
Severity: high/moderate
- Axios is Vulnerable to Denial of Service via __proto__ Key in mergeConfig
- Axios has a NO_PROXY Hostname Normalization Bypass that Leads to SSRF
- Axios has Unrestricted Cloud Metadata Exfiltration via Header Injection Chain
```

### Reproduction Steps

```bash
git clone https://github.com/awslabs/aws-crt-nodejs.git
cd aws-crt-nodejs
npm install --ignore-scripts
npm audit
```

### Possible Solution

Update the `axios` version in both `dependencies` and `overrides` in `package.json` from `^1.12.2` to `^1.15.1`, which is the first version that resolves all three vulnerabilities.

### Additional Information/Context

- `npm audit` confirms no axios vulnerabilities after updating to `1.15.1`.
- A fix for this is ready as a pull request.
- Long-term, issue #607 proposes replacing axios entirely with built-in Node.js alternatives.

### aws-crt-nodejs version used

1.21.0 (latest release)

### nodejs version used

v20.9.0

### Operating System and version

Ubuntu 20.04.5 LTS

Update the axios version in both dependencies and overrides in package.json, changing ^1.12.2 to ^1.15.1. Start by running npm install --ignore-scripts and npm audit as shown in the reproduction steps; done means npm audit no longer reports the three listed axios vulnerabilities.

Written by the indexing model from the issue text.