Security warnings should be shown by default

[daniel-beck]

plugin-installation-manager-tool/plugin-management-cli/src/main/java/io/jenkins/tools/pluginmanager/cli/CliOptions.java

Lines 77 to 80 in 79b38b4

	@Option(name = "--view-security-warnings",
	usage = "Show if any security warnings exist for the requested plugins",
	handler = BooleanOptionHandler.class)
	private boolean showWarnings;

There seems to be no real reason for this to be disabled by default.

--view-security-warnings should be made a no-op for compatibility, and a new option --hide-security-warnings (or similar) should be added to explicitly opt out of showing them.

[jiakuanghe]

Hi Mark,
@MarkEWaite I am planning to fix this issue.

My approach would be:

1. By default, the security warnings will display to the user. Although the user didn't use the option (--view-security-warnings), the result would still show.
2. Add a new option (--hide-security-warnings). For the users who want to hide the warnings.
3. Update the document in README.md
   3.1 Mark --view-security-warnings as deprecated
   3.2 Add option --hide-security-warnings

Do you think it sounds good?