[main] provisioning cluster: remove carriage returns from agentEnvVars values

[vardhaman22]

Issue:

rancher/rancher#50213

Problem

When configuring a provisioning cluster's agent environment variables from a file on UI, values containing DOS/Windows line endings (\r\n) retain the trailing carriage return.
These carriage returns are propagated to the generated node registration command, resulting in malformed environment variable values

Solution

Update the provisioning cluster mutating webhook to normalize agentEnvVars values during Create and Update operations.

The normalization removes trailing carriage return (\r) and newline (\n) characters while preserving any newline characters within the value.

CheckList

• Test
• Docs

[crobby]

Seems good. Is there any chance of \r or \n in the middle of the value that would need stripping or is this expected to be sufficient?

Also, is this change worthy of being noted in the mutator's doc?

[HarrisonWAffel]

Agree with Chad, we'll need to update the documentation as well. IIUC this was preventing users from registering nodes entirely, so I don't know if there are any migration / existing cluster concerns here, but something to think about

[vardhaman22]

Seems good. Is there any chance of \r or \n in the middle of the value that would need stripping or is this expected to be sufficient?

kept the behavior same except the line endings since the issue was reported explicitly for the line endings.