Various small fixes

[DL6ER]

What does this implement/fix?

This PR combines a few small changes I have distilled from user reports across Discourse over the past week, sorry for not putting them in separate PRs but they are rather small on their own.

List of changes:

• compile_filter_regex() should match case-insensitive (used by webserver.api.excludeDomains and webserver.api.excludeClients)
• Removed files.setupVars from pihole-FTL.toml as this path does not need to be configurable. I hard-wired the (likewise hard-wired) pre-v6.0 path
• Fix description of dns.rateLimit.count still referring to the old setting (RATE_LIMIT=1/3600 => dns.rateLimit.count=1 and dns.rateLimit.interval=3600)
• Fix description of webserver.api.allow_destructive mentioning the ability to shut down the system even though we don't offer this in v6.0
• Enlarge string buffer in get_web_port() as the 32 bytes may be too limiting and the final os may be clipped
• Ensure dns.cache.upstreamBlockedTTL = 0 actually causes discarding of upstream blocked queries
• Fix two copy-paste description errors in batchDelete for lists and groups

---

Related issue or feature (if applicable): N/A

Pull request in docs with documentation (if applicable): N/A

---

By submitting this pull request, I confirm the following:

1. I have read and understood the contributors guide, as well as this entire template. I understand which branch to base my commits and Pull Requests against.
2. I have commented my proposed changes within the code.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)

Checklist:

• The code change is tested and works locally.
• I based my code and PRs against the repositories developmental branch.
• I signed off all commits. Pi-hole enforces the DCO for all contributions
• I signed all my commits. Pi-hole requires signatures to verify authorship
• I have read the above and my PR is ready for review.