AWS CloudWatch Application Signals L2 Constructs for SLO

[liunia-amazon]

Description

Add L2 Constructs for AWS CloudWatch Application Signals SLO to simplify the creation of Application Signals SLO resources.
See #670 for
additional details.

Roles

Role	User
Proposed by	@liunia-amazon, @bjrara
Author(s)	@liunia-amazon
API Bar Raiser	@moelasmar
Stakeholders	@alias, @alias, @alias

See RFC Process for details

Workflow

• Tracking issue created (label: status/proposed)
• API bar raiser assigned (ping us at #aws-cdk-rfcs if needed)
• Kick off meeting
• RFC pull request submitted (label: status/review)
• Community reach out (via Slack and/or Twitter)
• API signed-off (label status/api-approved applied to pull request)
• Final comments period (label: status/final-comments-period)
• Approved and merged (label: status/approved)
• Execution plan submitted (label: status/planning)
• Plan approved and merged (label: status/implementing)
• Implementation complete (label: status/done)

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Author is responsible to progress the RFC according to this checklist, and
apply the relevant labels to this issue so that the RFC table in README gets
updated.