Raised from #2060

Simplify working with SharePoint URLs, so that if you've retrieved SharePoint URL in the past (which you can confirm by running m365 spo get), you no longer need to specify the host name and can use server-relative URLs instead and CLI prepends the host name ourselves. If you don't want to rely on auto-retrieving the SharePoint URL, you could preset it yourself using the m365 spo set command.

Spec:

• commands that right now require absolute URLs, support both absolute and relative URLs
• if a server-relative URL has been specified where an absolute URL is required, CLI automatically prepends the previously retrieved SharePoint host name
• if SharePoint URL has not been previously retrieved, CLI will fail with an error, asking user to either specify the SharePoint host name using m365 spo set or use absolute URLs
• specifying relative URLs should be enabled for all SPO commands and all options that require URLs
• ideally, the implementation is done centrally in the CLI right after resolving options and just before validating them