*.sh scripts / let reconcile_sylva_units use "sylvactl watch" with "--reconcile"

We need to add --reconcile to the sylva watch command that is used to trigger a refresh of the sylva-units HelmRelease.

If we don't then, on an upgrade that changes the source (e.g. an upgrade where the sylva-core commit changes):

• the sylva-units HelmRelease may be reconciled before its source is refreshed
• the source should be reconciled quickly-enough by Flux (because it's spec has been updated to point to the new sylva-core commit)
• ... but then, after the source is reconciled, nothing will refresh sylva-units, and nothing will happen until the next reconciliation (subject to the reconciliation period, by default 10 minutes)

This should solve issues like in https://gitlab.com/sylva-projects/sylva-core/-/jobs/7044079523#L304:

trigger reconciliation of sylva-units HelmRelease...
  helmrelease.helm.toolkit.fluxcd.io/sylva-units annotated
2024/06/07 12:33:15.307973 HelmRepository/sylva-core                          Static object - Ready
2024/06/07 12:33:15.307998 HelmChart/sylva-system-sylva-units                 ChartPackageSucceeded - packaged 'sylva-units' chart with version '0.0.0-git-3dff578f+2' and merged values files [values.yaml management.values.yaml use-oci-artifacts.values.yaml]
2024/06/07 12:33:15.308025 HelmRelease/sylva-units                            HelmChartNotReady - HelmChart 'sylva-system/sylva-system-sylva-units' is not ready: latest generation of object has not been reconciled
2024/06/07 12:33:16.372456 HelmRelease/sylva-units state changed: Progressing - Running 'upgrade' action with timeout of 5m0s
2024/06/07 12:33:16.372496  ╭╴Waiting for the following resources to progress:
2024/06/07 12:33:16.372501  │  HelmRelease/sylva-units               Progressing - Running 'upgrade' action with timeout of 5m0s
2024/06/07 12:33:16.372506  ╰╴╴╴┄
2024/06/07 12:34:13.032832 Command timeout exceeded
Timed-out waiting for the following resources to be ready:
    * HelmRelease/sylva-units: Progressing - Running 'upgrade' action with timeout of 5m0s

Because of failure https://gitlab.com/sylva-projects/sylva-core/-/jobs/7045102412#L265 on one of the pipeline of an early version of this MR, this MR also adjusts the timeout of the same sylvactl watch, and also makes this timer configurable via environment variables.

/cc @feleouet