Exempt Proofpoint's redirector from query string modifications

[fmarier]

Fixes brave/brave-browser#41134

Sec/privacy review: https://github.com/brave/reviews/issues/1751

Not the ideal long-term fix, but simple and easy to uplift.

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

1. Open https://urldefense.com/v3/__https://www.portainer.io/hs/preferences-center/en/direct?data=W2nXS-N30h-M1W45lXqV2nFX8ZW3SzKNq3gnnN0W4cQh6C1Bnn1kW1VjfB24fr2-BW4mm3dy3T2wkqW2MWfBj49z9PPW4mqs512qWTfrW4px5K71Nn7N2W32DKbz1V7s-qW21bSln2KWpS4W1SdHmq2YwgS9W3P8RNt2r6W8pW49QSSt1_tcPsW3GSrf749CfyJW2PPdX33JPrgmW4hcHf84hm-NmW2FS2pd2sMKL-W2YGYkz43RS-9W4pjpV52t0rxlW3SB_f94psLW2W3_Sm6w2FGVTjW3K2-cG4fzZLWW2qDSdB3bzPyBW3j8X_q2PMxWzW36CtK22MvcXrW4hNdFB3DLWP3W3VMWNy3SYMyvW1Vs-MC43NZJNW4hLsTd2B1T2JW2sB9wk3DMh2mW2D0QS-2t04tYW43Cpv42Tz6SwW32rgcB3_SfvDW4mq1yB36nnnkW3BNLQw2YfSH9W49sKsP3z4zKPW3zd1YL1Zm6S3W4kmj3Z2sQ7WVW36xkSD2RSm5hW1Q0SqC30sK9ZW2-kSbQ2nH5KcW36fNc_2RjGNjW36pblN43qsbhW2CCNvJ3_SL29W1_sQHx4fqK9NW3Sy1cb4mpD3h0&utm_campaign=XNF&utm_source=hs_automation&utm_medium=email&utm_content=264158909&_hsenc=p2ANqtz--9JvIgI266aB1UVizENwYNYREZSotsXOhWcMNeKjZLJO9ZwmR9xlyfsQN2orbT25IymZ_vKUNTANMKQMVQBnzowi2339ExVoOKMJaHx0t2yn5esgg&_hsmi=264158909__;!!MlclJBHn!0eDf-zTf69h-IhFT9WDu2GIXAtCy6RENwguPVpTF1k2K-Nbnzy1NXix2Gj7azc8yDFyI2z3Tz4nTFuGe2hlLzsBl$
2. Confirm it redirects to www.portainer.io instead of showing an error.