What this PR does / why we need it:

Introduce the possibility to use external secret for cluster scanner.
Currently it is possible to specify a global.sysdig.accessKeySecret for all the components besides the cluster scanner.

When using the external secret accessKeySecret the environment variable SYSDIG_ACCESS_KEY will look for the key access-key instead of sysdig_access_key, I did that in order to align with the other charts

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• Title of the PR starts with type and scope, (e.g. feat(agent,node-analyzer,sysdig-deploy):)
• Chart Version bumped for the respective charts
• Variables are documented in the README.md (or README.tpl in some charts)
• Check GithubAction checks (like lint) to avoid merge-check stoppers
• All test files are added in the tests folder of their respective chart and have a "_test" suffix

Check Contribution guidelines in README.md for more insight.