When using jsonPatches or strategicMergePatches in helmfile, the
`helm template` command was not receiving the `--kube-context` flag.
This caused issues when `--dry-run=server` was used (introduced in
PR #2271 to support lookup() functions), because helm would connect
to the wrong cluster context.
Root Cause:
1. `flagsForTemplate()` did not call `appendConnectionFlags()`, unlike
`flagsForUpgrade()` and `flagsForDiff()` which both include this call.
2. `processChartification()` did not include `--kube-context` when
setting `chartifyOpts.TemplateArgs` for internal helm template calls.
Fix:
1. Added `appendConnectionFlags()` call to `flagsForTemplate()` to ensure
kube-context and other connection flags are passed to helm template.
2. Added `getKubeContext()` helper function that resolves kube-context
with proper priority: release > environment > helmDefaults.
3. Modified `processChartification()` to include `--kube-context` in
chartifyOpts.TemplateArgs when chartify needs to run helm template.
4. Added compatibility check for `--validate` flag to avoid Helm 4
mutual exclusion error between --validate and --dry-run (Issue #2355).
Fixes#2309
Signed-off-by: Aditya Menon <amenon@canarytechnologies.com>