Moving logic that manipulates a ServeConfig into recievers on the
ServeConfig in the ipn package. This is setup work to allow the
web client and cli to both utilize these shared functions to edit
the serve config.
Any logic specific to flag parsing or validation is left untouched
in the cli command. The web client will similarly manage its
validation of user's requested changes. If validation logic becomes
similar-enough, we can make a serve util for shared functionality,
which likely does not make sense in ipn.
Updates #10261
Signed-off-by: Sonia Appasamy <sonia@tailscale.com>
c58c59ee54