fix(ksonnet): index-gateway make overrides configmap as var and antiAffinity

[sentoz]

fix(ksonnet): index-gateway make overrides configmap names and mount path as variables and antiAffinity

What this PR does / why we need it:

Fixes the problem that by specifying the variables _config.overrides_configmap_mount_name and
_config.overrides_configmap_mount_path, the name and path of the overrides configmap did not change.
And fixes the problem of not adding antiAffinity

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR

[sentoz]

Friends, I would like to see these changes.
@chaudum
@ashwanthgoli