[Backport 2024.2] fix(issue_cache): add pull-requests to cache

[mergify]

in some places we are using PRs and not issue to identify
if we should be skipping something in the test code

we now generate two diffrent cache files on s3 for each repository
one for the issues and one for the pull requests

client code is merging it to once local cache, so it's mentioning
of either one should be working as expect, and read from cache,
not using affecting the hourly rate-limit

Ref: https://github.com/scylladb/qa-tasks/issues/1735

Testing

• unit tests
• integration tests

PR pre-checks (self review)

• I added the relevant backport labels
• I didn't leave commented-out/debugging code

Reminders

• Add New configuration option and document them (in sdcm/sct_config.py)
• Add unit tests to cover my changes (under unit-test/ folder)
• Update the Readme/doc folder relevant to this change (if needed)

(cherry picked from commit 6661e26)

(cherry picked from commit 6f4b284)

Parent PR: #7850