feat: add RFC template for proposals

Author: heitorlessa

.github/ISSUE_TEMPLATE/feature_request.md

@@ -2,7 +2,7 @@
 name: Feature request
 about: Suggest an idea for this project
 title: ''
-labels: triage, feature-request
+labels: feature-request, triage
 assignees: ''
 
 ---

.github/ISSUE_TEMPLATE/rfc.md

@@ -0,0 +1,52 @@
+---
+name: RFC
+about: Feature design and proposals
+title: 'RFC: '
+labels: RFC, triage
+assignees: ''
+
+---
+
+## Key information
+
+* RFC PR: (leave this empty)
+* Related issue(s), if known: 
+* Area: (i.e. Tracer, Metrics, Logger, etc.)
+* Meet [tenets](https://awslabs.github.io/aws-lambda-powertools-python/#tenets): (Yes/no)
+
+## Summary
+[summary]: #summary
+
+> One paragraph explanation of the feature.
+
+## Motivation
+[motivation]: #motivation
+
+> Why are we doing this? What use cases does it support? What is the expected outcome?
+
+## Proposal
+[proposal]: #proposal
+
+> This is the bulk of the RFC.
+
+> Explain the design in enough detail for somebody familiar with Powertools to understand it, and for somebody familiar with the implementation to implement it.
+
+> This should get into specifics and corner-cases, and include examples of how the feature is used. Any new terminology should be defined here.
+
+## Drawbacks
+[drawbacks]: #drawbacks
+
+> Why should we *not* do this?
+
+> Do we need additional dependencies? Impact performance/package size?
+
+## Rationale and alternatives
+[rationale-and-alternatives]: #rationale-and-alternatives
+
+* **What other designs have been considered? Why not them?**
+* **What is the impact of not doing this?**
+
+## Unresolved questions
+[unresolved-questions]: #unresolved-questions
+
+> Optional, stash area for topics that need further development e.g. TBD