mmds: Smoother migration from v1 to v2

[zulinx86]

Reason / Changes

To allow easier migration from MMDS v1 to v2, made the following changes:

• Extends MMDS to support EC2 IMDS-compatible token headers (i.e. X-aws-ec2-metadata-token and X-aws-ec2-metadata-token-ttl-seconds).
• Adds an integration test that checks AWS SDK for Python (boto3) is able to get AWS credentials via MMDS out of the box.
• Makes MMDS versions 1 support token generation for the session-oriented method as in MMDS version 2. Note that MMDS version 1 continues to accept GET requests with invalid tokens or no token.
• Adds mmds.rx_invalid_token and mmds.rx_no_token metrics to allow users to keep track of the number of GET requests that were rejected in MMDS version 2. Even with MMDS version 1 configured, they also count GET requests that would be rejected under MMDS version 1.

Fixed some minor things

• Validates X-metadata-token-ttl-seconds header only if it is a PUT request to /latest/api/token.
• Rejectes X-Forwarded-For header in a case-insensitive way.

License Acceptance

By submitting this pull request, I confirm that my contribution is made under
the terms of the Apache 2.0 license. For more information on following Developer
Certificate of Origin and signing off your commits, please check
CONTRIBUTING.md.

PR Checklist

• I have read and understand CONTRIBUTING.md.
• I have run tools/devtool checkstyle to verify that the PR passes the
  automated style checks.
• I have described what is done in these changes, why they are needed, and
  how they are solving the problem in a clear and encompassing way.
• I have updated any relevant documentation (both in code and in the docs)
  in the PR.
• I have mentioned all user-facing changes in CHANGELOG.md.
• [ ] If a specific issue led to this PR, this PR closes the issue.
• [ ] When making API changes, I have followed the
  Runbook for Firecracker API changes.
• I have tested all new and changed functionalities in unit tests and/or
  integration tests.
• [ ] I have linked an issue to every new TODO.

---

• This functionality cannot be added in rust-vmm.

[codecov]

Codecov Report

Attention: Patch coverage is 97.24771% with 3 lines in your changes missing coverage. Please review.

Project coverage is 83.02%. Comparing base (ea87024) to head (6f4b604).
Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
src/vmm/src/rpc_interface.rs	84.61%	2 Missing ⚠️
src/vmm/src/device_manager/persist.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5290      +/-   ##
==========================================
+ Coverage   82.95%   83.02%   +0.06%     
==========================================
  Files         250      250              
  Lines       26879    26828      -51     
==========================================
- Hits        22298    22273      -25     
+ Misses       4581     4555      -26     

Flag	Coverage Δ
5.10-c5n.metal	83.47% <97.24%> (+0.01%)	⬆️
5.10-m5n.metal	83.45% <97.24%> (+<0.01%)	⬆️
5.10-m6a.metal	82.68% <97.24%> (+0.01%)	⬆️
5.10-m6g.metal	79.13% <97.24%> (+<0.01%)	⬆️
5.10-m6i.metal	83.45% <97.24%> (+0.01%)	⬆️
5.10-m7a.metal-48xl	82.66% <97.24%> (?)
5.10-m7g.metal	79.13% <97.24%> (+<0.01%)	⬆️
5.10-m7i.metal-24xl	83.42% <97.24%> (?)
5.10-m7i.metal-48xl	83.42% <97.24%> (?)
5.10-m8g.metal-24xl	79.12% <97.24%> (?)
5.10-m8g.metal-48xl	79.12% <97.24%> (?)
6.1-c5n.metal	83.51% <97.24%> (+0.01%)	⬆️
6.1-m5n.metal	83.51% <97.24%> (+0.01%)	⬆️
6.1-m6a.metal	82.72% <97.24%> (+0.01%)	⬆️
6.1-m6g.metal	79.13% <97.24%> (+0.01%)	⬆️
6.1-m6i.metal	83.51% <97.24%> (+0.01%)	⬆️
6.1-m7a.metal-48xl	82.72% <97.24%> (?)
6.1-m7g.metal	79.13% <97.24%> (+<0.01%)	⬆️
6.1-m7i.metal-24xl	83.52% <97.24%> (?)
6.1-m7i.metal-48xl	83.52% <97.24%> (?)
6.1-m8g.metal-24xl	79.12% <97.24%> (?)
6.1-m8g.metal-48xl	79.12% <97.24%> (?)

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[Manciukic]

LGTM!

         .
         _\____
        |_===__`.        ==/
        \/  '---"\ _ _ _ _/
  ______/_______/_|_|_|_|_|
_|--------------------==."
 \____________________.'  LGB
------------------------------------------------

[Manciukic]

Clippy is angry at you 🫨

error: this expression creates a reference which is immediately dereferenced by the compiler
   --> src/vmm/src/mmds/mod.rs:185:31
    |
185 |     match mmds.is_valid_token(&token) {
    |                               ^^^^^^ help: change this to: `token`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow
    = note: `-D clippy::needless-borrow` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::needless_borrow)]`

[zulinx86]

Clippy is angry at you 🫨

error: this expression creates a reference which is immediately dereferenced by the compiler
   --> src/vmm/src/mmds/mod.rs:185:31
    |
185 |     match mmds.is_valid_token(&token) {
    |                               ^^^^^^ help: change this to: `token`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow
    = note: `-D clippy::needless-borrow` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::needless_borrow)]`

Fixed! Sorry about that :(