Doc updates to include new FIPS Synthetics PL image

[nhyne]

What does this PR do? What is the motivation?

As a part of the FedRAMP High project the Synthetics team has built a new FIPS-compliant Private Location image. Customers who need FIPS compliance with the Datadog product will need to switch to using the new FIPS-compliant image.

Merge instructions

Eventually we would like to drop FIPS support from the current image. It is mentioned in a couple of places but this mention of disabling it would need to have a "after this version this flag is not supported" message. I am also curious if there's a pattern for a deprecation like this? As a part of the PR to update the removal of that flag would I also just add a note that PL versions after and including X.Y.Z are no longer FIPS compliant and customers must use the new image?

Merge readiness:

• Ready for merge

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Additional notes

[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/ajohnson/synth-18620/update-pl-docs-for-fips/synthetics/platform/private_locations/

[brett0000FF]

@nhyne - Thanks for the contribution! Main thing I fixed in my suggestion is the link that isn't rendering correctly (as you can see in the preview). The link has to be inside the site region partial. Once you apply this fix, I can approve. Thanks! 🚀

[brett0000FF]

@nhyne - Regarding your question about deprecation patterns: Our documentation typically reflects the current state of the product rather than maintaining detailed deprecation notices. When the FIPS support is removed from the current image, we would:

• Remove the mentions of the --disableFipsCompliance option
• Update documentation to clearly direct FIPS-requiring customers to use the dedicated FIPS-compliant image

We generally don't include version-specific deprecation notes unless there's a significant migration concern or customer impact that requires preserved documentation.