Document SECURE_LOG_LEVEL for IaC; align content across other feature areas

Problem to solve

SECURE_LOG_LEVEL is important for DIY debugging and is supported across Secure, including in IaC Scanning. However, the IaC Scanning docs page doesn't mention it.

There are also a number of different presentations of SECURE_LOG_LEVEL across the docs.

Further details

• Mentions of the variable in docs today.

Proposal

We should:

• Mention the variable for IaC Scanning.
• Align how the variable is presented so that we have one high-quality source of truth about the variable and how to use it.

The content should indicate that which log levels are available depends on the analyzer, but that the values are standardized across analyzers.

Who can address the issue

Anyone should be able to address this.

Other links/references

• trace log level is mentioned in this issue: Document Static Analysis usage of trace log level. (#356476 - closed)
• This was discussed in Slack (team members only)