Add Cisco vIOS L2 support

[tjbalzer]

All necessary changes needed to make the vios files work for vIOSL2.

Changes compared to code for vios router support

Added new directory viosl2 (was quicker than changing the vios code and making it work for vios and viosl2 ;-)).

Makefile

• Adapt NAME to vIOSL2
• Adapt comments and version regex for viosl2 image file

Dockerfile

Added procps to base bookworm image for troubleshooting purposes.

launch.py

• Increase memory for IOSvL2 image from 512 to 768
• Change expected prompt from Router> to Switch>
• Adapt initial configuration for L2 switches

README.md

All changes needed to describe viosl2 instead of vios.

Testing

Successful tests with image vios_l2-adventerprisek9-m.ssa.high_iron_20200929.qcow2 (CML reference platform). Tested with example topology file shown in README.md and also with a 10 node network with core, distribution and access switches incl. access vlans, transport vlans, trunk ports, OSPF and HSRP (incl. interface tracking, which is not available in IOL L2).

[kaelemc]

Did a quick test. Looks all good, should be good to go!