doc: Add Rancher Turtles uninstallation notes

[furkatgofurov7]

Related to: rancher/turtles#425

[furkatgofurov7]

This needs to be on hold until rancher/turtles#425 is merged

[furkatgofurov7]

@richardcase @Danil-Grigorev thanks folks for reviews, updated now.

[furkatgofurov7]

@richardcase @Danil-Grigorev after discussing this with @salasberryfin and giving it another thought, maybe we need to extend the current PR a bit. In reality, user can uninstall extenstion in 2 ways:

1. Extension installed via Rancher Manager (local cluster=>adding repo=>installing chart). By default, cleanup is enabled and when user uninstalls the chart from Rancher Manager, it should be uninstalled (covered in this PR)
2. Extension installed via helm command. By default, cleanup is enabled and when user uninstalls the chart using helm uninstall, it should be uninstalled (not covered)

Does it make sense to note both options in this PR, WDYT?

[richardcase]

Does it make sense to note both options in this PR, WDYT?

I think we should cover both options.

[furkatgofurov7]

@richardcase @Danil-Grigorev after discussing this with @salasberryfin and giving it another thought, maybe we need to extend the current PR a bit. In reality, user can uninstall extenstion in 2 ways:

1. Extension installed via Rancher Manager (local cluster=>adding repo=>installing chart). By default, cleanup is enabled and when user uninstalls the chart from Rancher Manager, it should be uninstalled (covered in this PR)
2. Extension installed via helm command. By default, cleanup is enabled and when user uninstalls the chart using helm uninstall, it should be uninstalled (not covered)

Does it make sense to note both options in this PR, WDYT?

This is how it looks after recent changes:

[furkatgofurov7]

This needs to be on hold until rancher-sandbox/rancher-turtles#425 is merged

425 is merged, and this should be unblocked now

[furkatgofurov7]

Pushed 9c59f83 to update values.md with new options.

[furkatgofurov7]

@richardcase @salasberryfin updated now, PTAL