Add Snap allowlist process issue templates

.github/ISSUE_TEMPLATE/block-snap.md

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+---
+name: Block a Snap
+about: Required for blocking an existing Snap (still listed in the registry but not accessible)
+title: '[Block Snap] Name of Snap here'
+labels: allowlist,allowlist-block-snap
+assignees: ''
+---
+
+## Description
+
+Note: Blocking a Snap means that both new and existing users cannot use the Snap.
+
+## Checklist
+
+All items in the list below needs to be satisfied.
+
+- [ ] Is the reason for the block documented in this issue?
+- [ ] The corresponding pull request in this repo has been merged.

.github/ISSUE_TEMPLATE/new-snap.md

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+---
+name: New Snap
+about: Required for every new Snap
+title: '[New Snap] Name of Snap here'
+labels: allowlist,allowlist-new-snap
+assignees: ''
+---
+
+## Checklist
+
+All items in the list below needs to be satisfied.
+
+- [ ] Is the Snap repository publicly accessible and linked in this ticket?
+- [ ] Is the Snap distributed on [npm](https://www.npmjs.com/) and linked in this ticket?
+- [ ] Has an audit been performed and the audit report attached or linked in this issue?
+- [ ] Is a complete list of discovered vulnerabilities from the audit documented in this issue?
+- [ ] For vulnerabilities that have been deemed necessary to be addressed, are the links to the fixes attached to this issue?
+- [ ] For vulnerabilities that have been deemed not necessary to be addressed, is a reason for each of them documented in this issue?
+- [ ] The corresponding pull request in this repo has been merged.

.github/ISSUE_TEMPLATE/remove-snap.md

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+---
+name: Remove a Snap
+about: Required for removing an existing Snap from the registry
+title: '[Remove Snap] Name of Snap here'
+labels: allowlist,allowlist-remove-snap
+assignees: ''
+---
+
+## Description
+
+Note: Removing a Snap from the registry means that users who have installed the Snap may continue to use it. New users will not be able to install the Snap.
+
+## Checklist
+
+All items in the list below needs to be satisfied.
+
+- [ ] Is the reason for the removal documented in this issue?
+- [ ] Are the key parts of the communication with the developer to remediate the concerns documented in this issue?
+- [ ] The corresponding pull request in this repo has been merged.

.github/ISSUE_TEMPLATE/update-snap.md

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+---
+name: Update a Snap
+about: Required for every update for a Snap
+title: '[Update Snap] Name of Snap here'
+labels: allowlist,allowlist-update-snap
+assignees: ''
+---
+
+## Checklist
+
+All items in the list below needs to be satisfied.
+
+- [ ] Is the summary of the change documented in this ticket?
+- [ ] Has a MetaMask Snaps team member reviewed whether the changes need to be vetted?
+- [ ] If there are changes that need to be vetted, attach a description and the relevant fixes/remediations to this issue.
+- [ ] The corresponding pull request in this repo has been merged.