SCI Service Mapping split by language

[clreaume]

What does this PR do? What is the motivation?

refactors the Service Mapping documentation from a single large page into a multi-page structure organized by language. the original service-mapping.md (394 lines) was replaced with:

• a new _index.md landing page with high-level overview and logo grid linking to the new child pages
• eight language-specific child pages: Java, Python, Go, Node.js, Ruby, PHP, .NET, and an "Other" catch-all
• navigation entries added to main.en.yaml for each new page

I also made a minor fix to the collapse-content.html shortcode to allow for code formatting in subject text

it's also worth noting that on each of the eight language-specific children, I created a "Prerequisites" section that includes:

• "Datadog Agent v7.35.0 or later is required." (currently in the Overview of the main page )
• each language's client library requirement (currently in a Note callout on each language's tab )
• a link to the Build inside a Docker container section, left on the top-level page

Merge readiness

• Ready for merge

AI assistance

Used Claudina

Additional notes

n/a

[github-actions]

Preview links (active after the build_preview check completes)

New or renamed files

• https://docs-staging.datadoghq.com/cara/DOCS-14939_SCI-service-mapping-split-by-language/source_code/service-mapping/
• https://docs-staging.datadoghq.com/cara/DOCS-14939_SCI-service-mapping-split-by-language/source_code/service-mapping/dotnet
• https://docs-staging.datadoghq.com/cara/DOCS-14939_SCI-service-mapping-split-by-language/source_code/service-mapping/go
• https://docs-staging.datadoghq.com/cara/DOCS-14939_SCI-service-mapping-split-by-language/source_code/service-mapping/java
• https://docs-staging.datadoghq.com/cara/DOCS-14939_SCI-service-mapping-split-by-language/source_code/service-mapping/nodejs
• https://docs-staging.datadoghq.com/cara/DOCS-14939_SCI-service-mapping-split-by-language/source_code/service-mapping/other
• https://docs-staging.datadoghq.com/cara/DOCS-14939_SCI-service-mapping-split-by-language/source_code/service-mapping/php
• https://docs-staging.datadoghq.com/cara/DOCS-14939_SCI-service-mapping-split-by-language/source_code/service-mapping/python
• https://docs-staging.datadoghq.com/cara/DOCS-14939_SCI-service-mapping-split-by-language/source_code/service-mapping/ruby

Removed or renamed files (these should redirect)

• https://docs-staging.datadoghq.com/cara/DOCS-14939_SCI-service-mapping-split-by-language/source_code/service-mapping