Trim user input where applicable

[jacklul]

By submitting this pull request, I confirm the following:

• I have read and understood the contributors guide, as well as this entire template.
• I have made only one major change in my proposed changes.
• I have commented my proposed changes within the code.
• I have tested my proposed changes.
• I am willing to help maintain this change if there are issues with it later.
• I give this submission freely and claim no ownership.
• It is compatible with the EUPL 1.2 license
• I have squashed any insignificant commits. (git rebase)
• I have Signed Off all commits. (git commit --signoff)

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What does this PR aim to accomplish?:

Make life easier for people who copy & paste values into fields.

Trims user input fields:

• groups-clients.php view
  • #ip-custom field (groups-client.js:254), it's trimmed in groups.php:242 so it doesn't make sense to not trim it here
• settings.php?tab=dns view
  • conditionalForwardingIP and conditionalForwardingDomain
  • custom DNS fields
• settings.php?tab=piholedhcp view
  • from, to, router, domain, leasetime
  • AddMAC, AddIP, AddHostname
• dns_records.php view
  • ip and domain

Some of those changes were in #825 but the PR was closed.

How does this PR accomplish the above?:

Added trim() calls in appropriate places

What documentation changes (if any) are needed to support this PR?:

None

I think I got all of them ? Other fields (whitelist/blacklist) are trimmed already.

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/pi-hole-5-1-released/35577/1