task: Replace Axios with native Fetch

[toufali]

Because

Axios continues to be flagged with high vulnerabilities and maintaining the extra dependency is time-consuming

This pull request

replaces Axios with native fetch.

Issue that this pull request solves

Closes: FXA-11465
Closes: FXA-11503

Checklist

Put an x in the boxes that apply

• My commit is GPG signed.
• If applicable, I have modified or added tests which pass locally.
• I have added necessary documentation (if appropriate).
• I have verified that my changes render correctly in RTL (if appropriate).

Other information (Optional)

• native fetch is already the dominant HTTP request API used throughout the codebase.
• TODO: fix broken tests

In a couple instances, custom agents are created and passed to Axios via the "agent" option, to allow advanced connection management. Native fetch does not include this option. Connection reuse is handled internally via undici, which is suggested to be highly optimized for performance and connection pooling out-of-the-box.

Rather than remove the Axios-enabled advanced connection management, I resorted to using node-fetch in these instances, instead of native fetch. node-fetch is already a dependency of ours, and exposes the "agent" option for connection management. Should we decide that undici's connection reuse provides enough performance, we can remove the agents and use native fetch instead of node-fetch.

[vpomerleau]

@toufali should we close this PR for now?