Shouldn't be able to set validation-failed gateway strings

[stephendonner]

Description

Shouldn't be able to set validation-failed gateway strings.

Found while testing #16999.

Steps to Reproduce

1. new profile
2. launch Brave
3. load brave://settings/ipfs
4. click on the Change button for IPFS public gateway fallback
5. enter https://blah
6. click Submit
7. notice the error message
8. cancel the dialog
9. look at the value in brave://settings/ipfs for IPFS public gateway address

Actual result:

I was able to set https://blah as the gateway host, even though it failed validation.

example	example	example

Expected result:

Should still be the default https://dweb.link after throwing the error message.

Reproduces how often:

100%

Brave version (brave://version info)

Brave	1.30.38 Chromium: 93.0.4577.51 (Official Build) nightly (x86_64)
Revision	762d21050e2da59930c784c09b134d0b0b148188-refs/branch-heads/4577@{#915}
OS	macOS Version 11.5.2 (Build 20G95)

/cc @spylogsster @lidel

[stephendonner]

Verified PASSED using the inline test plan with

Brave	1.30.42 Chromium: 93.0.4577.51 (Official Build) nightly (x86_64)
Revision	762d21050e2da59930c784c09b134d0b0b148188-refs/branch-heads/4577@{#915}
OS	macOS Version 11.5.2 (Build 20G95)

Steps:

1. new profile
2. launched Brave
3. loaded brave://settings/ipfs
4. clicked on the Change button for IPFS public gateway fallback
5. entered https://blah
6. clicked Submit

Confirmed I received Invalid gateway address error message in the dialog, and the Submit button didn't do anything.

---

Verified PASSED using

Brave	1.30.63 Chromium: 93.0.4577.63 (Official Build) beta (64-bit)
Revision	ff5c0da2ec0adeaed5550e6c7e98417dac77d98a-refs/branch-heads/4577@{#1135}
OS	Linux

Steps:

1. new profile
2. launched Brave
3. loaded brave://settings/ipfs
4. clicked on the Change button for IPFS public gateway fallback
5. entered https://blah
6. clicked Submit

Confirmed I received Invalid gateway address error message in the dialog, and the Submit button didn't do anything.

[LaurenWags]

Updated to release-notes/exclude per discussion with @rebron and @kjozwiak