Bug 32118: Add optional support for `:` as the modifier

Bug 32118: Add optional support for `:` as the modifier

This patch adds optional support for using `:` as the modifier for
invoking the 'count' method for relations as discussed.

We retain support for `+` for backward compatability to prevent a
breaking change.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 64d3498da4c62f8a2fa3d28c7cfe8b0a9e251288)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>