refactor(kubeaid-agent): make the exporters local subcharts

[ashish1099]

Moves the two exporters into charts/security-exporter and charts/backup-exporter, each with its own Chart.yaml, values.yaml and templates/. The parent's templates/ drops from 26 files to 8, and its values.yaml from 584 lines to 170.

They resolve from the working tree: no repository field, no Chart.lock, no helm dependency update. This is NOT the pattern used for vendored upstream charts, where the source is checked in twice -- nothing here is duplicated.

Two bugs the flat layout had introduced come out in the wash, both invisible until now because backup-exporter defaults to off:

• Its image tag is restored. image.tag defaults to .Chart.AppVersion, which after the fold-in was kubeaid-agent's "0.0.3" rather than backup-exporter's own "v1.2.2" -- so enabling it would have pulled a tag that does not exist. The subchart carries its original version and appVersion again.
• Its container was named kubeaid-agent, from .Chart.Name. Inside a subchart that is backup-exporter, which is also why app.kubernetes.io/name -- the label kubeaid-agent and kubeaid-cli discover this exporter by -- is now correct by construction instead of pinned by hand.

Values keys follow the subchart names: securityExporter -> security-exporter, backupExporter -> backup-exporter. An alias would have kept the old camelCase, but it rewrites .Chart.Name to the alias too, which puts that discovery label back at risk; the rename is the safer trade.

The promtool workflow follows the templates into the subchart and now enables backup-exporter explicitly, since the rules no longer render by default.

Verified by rendering master and this branch and diffing the objects: same 16 objects by default and 25 with backup-exporter enabled, none missing, none new, and no difference beyond metadata.labels -- where helm.sh/chart now names the subchart -- plus the two backup-exporter fixes above.