Feat/arch diagram update

[rajat-amzn]

Issue #, if available: NA

Description of changes:

Updated the architecture diagram with the latest AWS Lambda logo.

• Replaced the old architecture diagram PNG (FAST-architecture-20260302.png) with an updated version (FAST-architecture-20260403.png)
• Updated the .drawio source file to reflect the updated diagram

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[kaleko]

Diagram looks great! Would you mind doing the following in this PR:

1. Remove the old diagram (png and drawio)
2. Update all the READMEs etc which reference the old diagram (a "grep" should find them, it might only be the top level one TBH)
3. Add your name to the CONTRIBUTORS file (optional, feel free to do so if you'd like)

[rajat-amzn]

Thanks for the comments David.

1. The old png is already removed, drawio is getting overwritten with updated verison.
2. Updated the README, was referenced in top level only.
3. Added both to contributors and changelog (unreleased).