Cylc-flow: symlink dirs: move into [install] section

[oliver-sanders]

The [symlink dirs] section applies only to the cylc install command, propose moving it into the [install] section.

For reference the config tree currently looks like so:

>>> from cylc.flow.cfgspec.globalcfg import SPEC
>>> print(SPEC.tree())
global.cylc
    ...
    [install]
        source dirs
    ...
    [symlink dirs]
        [<install target>]
            run
            log
            share
            share/cycle
            work

Pull requests welcome!

[MetRonnie]

So it would be [install][symlink dirs][<install target>]...? Can't see any reason not to

[dpmatthews]

The [symlink dirs] section applies only to the cylc install command

Also used by cylc play (as part of remote init)

[datamel]

In my mind, I think it makes sense to move [symlink dirs] into the install section, even though it is used by cylc play. I can see see the install section as a setup type section, that deals with installation of files for a workflow. Rather than being only strictly used for cylc install?