Tiny documentation update

Hi,

could you please make a tiny documentation update for [influxdb2 helm chart](https://github.com/influxdata/helm-charts/blob/734b06fef3a98891b03066b375d0168b933322d0/charts/influxdb2/templates/NOTES.txt#L17)?
I just spend a day on trying to figure out why I am not able login to UI until I realized that I did not correctly understand the Note in helm chart:

```
Note: with enabled persistence, admin password is only set once during the initial deployment. The password is not changed when InfluxDB 2 is re-deployed with different password.
```

I thought that under re-deployment you mean uninstall/install, and not that I have to also delete related pvc as it is not automatically deleted during helm uninstall, i.e.:

```
mulinka@saiacheron:~$ helm uninstall influx -n influx
These resources were kept due to the resource policy:
[PersistentVolumeClaim] influx-influxdb2

release "influx" uninstalled
```

so I was "re-deploying", i.e. uninstalling/installing/upgrading but none of it made any difference as the initial pvc with initial random password was always being used.

Could you please either (i) fix the user/pass update when the deployment is updated? or (ii) change the helm chart note to something like:

```
Note: with enabled persistence, admin password is only set once during the initial deployment. The password is not changed when InfluxDB 2 is re-deployed with different password. You **HAVE TO** delete the pvc in order to change the admin password!
```

Open charts/influxdb2/templates/NOTES.txt at the referenced line and read how the current persistence and password behavior is described. Update the note so it clearly explains that the retained PVC preserves the initial admin password and check the rendered Helm notes to confirm the warning is unambiguous.

Written by the indexing model from the issue text.