fix: shorten instance id (#391)

* fix: shorten instance id

* chore: update docs

* chore: update merged manager lib

docs/how-to/openstack-runner.md

@@ -57,3 +57,6 @@ The `openstack-network` configuration sets the network used to create the OpenSt
 Note that the network should be configured to allow traffic from the charm deployment (Juju machine) to the OpenStack virtual machine, and traffic from the OpenStack virtual machine to GitHub.
 
 The network documentation is [here](https://docs.openstack.org/neutron/latest/admin/intro-os-networking.html).
+
+> NOTE: The name of the application must not be longer than 50 characters. A valid runner name is 64 characters or less in length and does not include '"', '/', ':',
+'<', '>', '\', '|', '*' and '?'. 14 characters are reserved for Juju unit number and unique identifier.