Add exempt-issue-types option for blocklist filter by issue type

[veryfancy]

Description:

Introduce a parameter exempt-issue-types that ensures that issues from a list of types will not be marked stale or closed.

This is a blocklist counterpart to the allowlist option only-issue-types added in:

• Filter based on issue type #1187

Related issue:

• Support exempt-issue-types option #1293

Check list:

• Mark if documentation changes are required.
• Mark if tests were added or updated to cover the changes.

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[maxwxyz]

@luketomlinson this is similar to #1255

[Bibo-Joshi]

Hi. As a heads-up, I see that main.ts was not updated, which will probably lead to the input being ignored. See #1298, were I discovered that for only-issue-types :)

[veryfancy]

@Bibo-Joshi Thank you for the heads-up. I updated main.ts to include input reading for exemptIssueTypes. I included onlyIssueTypes as well, in case this merges first (and because I suspect it might prevent a merge conflict if your PR merges first).

[Bibo-Joshi]

Sweet :)