Mirrors the existing `supervisor.serviceAccount` pattern onto webapp so
operators can annotate the SA (IRSA `eks.amazonaws.com/role-arn`,
Workload Identity, etc.) or bring their own SA. Without this,
`webapp.serviceAccount.annotations` isn't exposed and operators have to
patch the SA out-of-band.
```yaml
webapp:
serviceAccount:
create: true
name: ""
annotations:
eks.amazonaws.com/role-arn: arn:aws:iam::123456789012:role/trigger-webapp
```
Three pieces, same as supervisor:
- `webapp.serviceAccount.create` toggle on the SA block
- `webapp.serviceAccount.annotations` + `name` values
- `trigger-v4.webappServiceAccountName` helper, used by the SA, the
token-syncer RoleBinding subject, and the Deployment's
`serviceAccountName`
Role + RoleBinding are left unguarded (matching supervisor's shape where
`rbac.create` is a separate toggle from `serviceAccount.create`) -
BYO-SA users take on the responsibility of ensuring the SA they supply
has the permissions the RoleBinding grants.
Verified with `helm template` against default values, an IRSA annotation
override, and `create: false` with a custom name.
nicktrn
87b6716535