Verbiage tweaks for SAST config MRs

What does this MR do?

This adds clarification to the difference between adding SAST when no CI has been set up before, versus when ADO has been running.

This work is being done in support of this issue, and specifically this linked comment: #223878 (comment 378642977)

Note: We will be moving away from this REST approach with this upcoming issue: BE implementation - Convert Rest API to GraphQL mutation for MR Creation flow

Screenshots

SAST commit message and description >>

SAST .gitlab-ci.yml commit >>

ADO commit message and description >>

ADO .gitlab-ci.yml commit >>

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team