[v17] Apply the _DISABLE_AWS_FIPS setting to iam and stscreds

[codingllama]

Backports #52065 and #52123 to branch/v17.

#52123 is needed so we can address all stscreds.NewCredentials calls without an import cycle.

This PR includes commits unique to branch/v17, as AWS SDK use differs from master.

Changelog: Applied TELEPORT_UNSTABLE_DISABLE_AWS_FIPS to iam and stscreds

[codingllama]

Commit breakdown:

• New files are cherry-picked without changes (90be958, 5352168)
• "Use iamutils" deviates due to SDK use (f30c443)
• "Use stsutils" is a clean cherry-pick (506c14a), but it misses an occurence fixed by a later commit
• .golangci.yml had conflicts, but nothing complicated (4ce9f9a)
• daf8868 is a cherry-pick from Move IsFIPSDisabledByEnv to lib/utils/aws/awsfips #52123
• All commits after daf8868 / "Move IsFIPSDisabledByEnv" are new to this branch. They address missing stscreds.NewCredentials, iam.New calls (SDKv1, not present on master) and add more forbidigo rules.

[codingllama]

I'll do branch/v16 and branch/v15 backports based on this one. I expect further conflicts, but hopefully nothing too different from what we've seen here. If there is anything noteworthy on other branches I'll call it out specifically.

[codingllama]

Friendly ping @nklaassen ?