Add SOCRadar to TAXII 2 recommended configurations and sources list

[Radargoger]

Purpose of this pull request

Adds SOCRadar to the STIX/TAXII 2 Client Source documentation:

• Adds SOCRadar TAXII Client to the TAXII 2 sources bullet list.
• Adds a SOCRadar row to the Recommended configurations table linking to socradar-config.json (added in Add SOCRadar TAXII 2 sample configuration (socradar-config.json) #6621), explaining Basic authentication, the Discovery URL (https://taxii2.socradar.com/taxii2/), and the three API roots (radar_alpha, radar_gamma, radar_premium).
• Includes guidance on how to obtain TAXII credentials — by contacting SOCRadar at support@socradar.io or via the SOCRadar Platform.

Depends on #6621 — that PR must be merged first to avoid a broken link to socradar-config.json.

Select the type of change

• Minor Changes - Typos, formatting, slight revisions
• Update Content - Revisions, updating sections
• New Content - New features, sections, pages, tutorials
• Site and Tools - .clabot, version updates, maintenance, dependencies, new packages for the site (Docusaurus, Gatsby, React, etc.)

Ticket (if applicable)

N/A

[cla-bot]

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[Radargoger]

Hi reviewers — please merge #6621 first, otherwise this PR will introduce a broken link to socradar-config.json. Thanks!

[cla-bot]

Thank you for your contribution! As this is an open source project, we require contributors to sign our Contributor License Agreement and do not have yours on file. To proceed with your PR, please sign your name here and we will add you to our approved list of contributors.

[jpipkin1]

@Radargoger, thank you for your submission!

This pull request submits a change directly to the main branch, rather than placing it in a separate branch. We do not support this approach, since it puts the main branch at risk. Please resubmit your change in its own branch (that is, in a fork) as described in the article Create or Edit a Doc in our Contribution Guide.

[jpipkin1]

Thank you for your contribution! As this is an open source project, we require contributors to sign our Contributor License Agreement and do not have yours on file. To proceed with your PR, please sign your name here and we will add you to our approved list of contributors.

@Radargoger, thank you for signing our Contributor License Agreement. It looks like you have signed it multiple times. You do not need to sign it again

[Radargoger]

Superseded by #6633, which uses a proper feature branch as requested by the reviewers.