feat: Added support for Squadcast provider

[Lucifer8729]

Squadcast is an incident management platform built on DevOps & SRE best practices to help you adopt the same to simplify incident management, get meaningful notifications, and enable faster incident resolution in collaboration. Explore all the incredible SRE features and incident resolution capabilities in this documentation.
Squadcast unites on-call alerting and incident management along with SRE workflows under one platform. Automate and revamp your incident response process and refine service expectations by learning continuously from past incidents using one simple, integrated, affordable, and customizable platform.

• Homepage

This PR adds Squadcast as a provider with the support of the following resources:

• deduplication_rules
• escalation_policy
• routing_rules
• runbook
• service
• slo
• squad
• suppression_rules
• tagging_rules
• team
• team_member
• team_roles
• user

[google-cla]

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[Lucifer8729]

As this is my first time contributing to the repo, @sergeylanzman can you take a look at the workflow approval, please?

[Lucifer8729]

@sergeylanzman can you take a look at the workflow approval, please?
I have fixed the golangci-lint errors.

[raghuchinnannan]

Just a reminder, in case if it was missed...

@sergeylanzman Could you please take a look at the PR and approve the workflows?

Thanks in advance.