Provide common issue triage guide for O3DE

[lmbr-pip]

In community, add a general issue triage guide that can be used/reference by all SIGS. Related to o3de/tsc#15

Guide:

• Creates common expectations around issue triage practices
• Documents expectations around common label settings

Prevents each SIG creating highly divergent processes and label usage and avoids duplication of content. SIGs can then just own the delta/differences in the SIG specific issue guides.

[lmbr-pip]

@forhalle - At one point you were going to contribute a standard triage guide. Is that still planned?

[lmbr-pip]

I made an initial PR of Halle's issue triage guide: #146