api: Add SetRootCAsFromPEM method

[prziborowski]

Add SetRootCAsFromPEM to allow passing in-memory PEM-encoded certificates instead of requiring them to be on disk. This is useful for read-only filesystems where CA contents are already available in memory.

Description

Add SetRootCAsFromPEM to allow passing in-memory PEM-encoded
certificates instead of requiring them to be on disk. This is
useful for read-only filesystems where CA contents are already
available in memory.

How Has This Been Tested?

Tested with a container doing:

	if len(config.CAContents) != 0 {
		if err = soapClient.SetRootCAsFromPEM([][]byte{config.CAContents}); err != nil {
			return fmt.Errorf("failed to set root CA %s: %w", config.CAFilePath, err)
		}
	}

and was able to connect to vCenter properly.

Guidelines

Please read and follow the CONTRIBUTION guidelines of this project.

[hickeng]

Up to @prziborowski whether to change validation of empty slice or not.