Update SBOM reference to monorepo and connectors to be on demand

[maxdanilov]

Description

As discussed with @MaxTru, due to the current process of SBOM generation not done automatically, and FOSSA becoming the SBOM solution in the future to auto-generate the SBOMs in the future as a part of the release process (TBD), it makes sense to replace the confusing SBOM links for the camunda/camunda with the disclaimer that they can be generated on demand.

The SBOMs for camunda/connectors are still generated the old way (still to be converted to FOSSA generation in the future), so I kept the text there as is.

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support. (add bug or support label)
• This is already available but undocumented and should be released within a week. (add available & undocumented label)
• This is on a specific schedule and the assignee will coordinate a release with the DevEx team. (create draft PR and/or add hold label)
• This is part of a scheduled alpha or minor. (add alpha or minor label)
• There is no urgency with this change (add low prio label)

PR Checklist

• My changes are for an upcoming minor release and:
  • are in the /docs directory (version 8.8).
  • are in the /versioned_docs/version-8.7/ directory (version 8.7).
• My changes are for an already released minor and are in a /versioned_docs directory.

• I added a DRI, team, or delegate as a reviewer for technical accuracy and grammar/style:
  • Engineering team review
  • Technical writer review via @camunda/tech-writers unless working with an embedded writer.

[maxdanilov]

Follow-up issues:

• Release: automatically generate SPDX SBOMs camunda#29270
• Automatically generate SPDX SBOMs connectors#4198
• https://github.com/camunda/web-modeler/issues/13429 - not sure this should be done as it's not public repository, but let's keep it just in case.

[MaxTru]

Thanks @maxdanilov.

As another follow-up and clean-up activity, should we delete https://github.com/camunda/camunda/blob/main/.github/workflows/sbom.yml?

[maxdanilov]

As another follow-up and clean-up activity, should we delete https://github.com/camunda/camunda/blob/main/.github/workflows/sbom.yml?

Yep, good point, I've included this step in camunda/camunda#29270