Improve verifiable conversion regex

[btlechowski]

Correctly verifiable conversion regex works, but can be improved.
Regex was introduced in: https://github.com/brave/brave-core/pull/9089/files
Improvement suggested by @iambrianfung

Steps to Reproduce

1. Check verifiable conversion regex

Actual result:

Regex is "^[a-zA-Z0-9/-]*$"

Expected result:

Regex is "^[-a-zA-Z0-9]*$"

Reproduces how often:

Easily reproduced

Brave version (brave://version info)

Brave	1.27.105 Chromium: 92.0.4515.93 (Official Build) (64-bit)
Revision	6eb43ff7850a1d710c3f827a0555737c74edab5c-refs/branch-heads/4515@{#1378}
OS	Ubuntu 18.04 LTS

cc @jsecretan @iambrianfung @tmancey

[iambrianfung]

@tmancey
did a bit of searching around. it seems that the Golang regex checkers should be sufficiently good for our purposes. that being because re2 is developed by Google, as is Golang.
https://pkg.go.dev/regexp links to https://github.com/google/re2/wiki/Syntax
maybe the simplest way is to add a test against the strings foo-1234/, /foo-1234, foo/1234 and see that they should fail with ^[-a-zA-Z0-9]*$ but not ^[a-zA-Z0-9/-]*$
i also noticed that ^[a-zA-Z0-9-]*$ also works

[btlechowski]

Verification passed on

Brave	1.29.74 Chromium: 93.0.4577.58 (Official Build) (64-bit)
Revision	c4410ece044414ea42fa4ba328d08195e818a99c-refs/branch-heads/4577@{#1076}
OS	Linux

Verified for conversion id qa123

Verified conversion was scheduled

[25430:25430:0829/062643.124868:VERBOSE1:conversions.cc(322)] Conversion for campaign id 8b30cb36-e5d4-460b-9e95-3199d80720bb, creative set id 46fde2a5-3cef-4960-bd77-36af52eb3192, creative instance id e793e5b5-c073-4ceb-8174-f5462d782d95 and advertiser id 9db2f01d-07d4-409b-a017-8415c80df432 on Sunday, August 29, 2021 at 6:26:43 AM
[25430:25430:0829/062643.158986:VERBOSE6:conversions.cc(375)] Successfully logged conversion event
[25430:25430:0829/062643.160440:VERBOSE3:conversions.cc(398)] Successfully appended conversion to queue
[25430:25430:0829/062643.167148:VERBOSE1:conversions.cc(503)] Convert campaign id 8b30cb36-e5d4-460b-9e95-3199d80720bb, creative set id 46fde2a5-3cef-4960-bd77-36af52eb3192, creative instance id e793e5b5-c073-4ceb-8174-f5462d782d95 and advertiser id 9db2f01d-07d4-409b-a017-8415c80df432 in 4 hours, 49 minutes, 47 seconds at 11:16 AM

Verified the conversion queue contains the conversion id

Verified the envelop has been attached to the confirmation

Verified for conversion id qa-123

Verified conversion was scheduled

[28748:28748:0829/224122.376338:VERBOSE1:conversions.cc(322)] Conversion for campaign id 8b30cb36-e5d4-460b-9e95-3199d80720bb, creative set id 46fde2a5-3cef-4960-bd77-36af52eb3192, creative instance id e793e5b5-c073-4ceb-8174-f5462d782d95 and advertiser id 9db2f01d-07d4-409b-a017-8415c80df432 on Sunday, August 29, 2021 at 10:41:22 PM
[28748:28748:0829/224122.394146:VERBOSE6:conversions.cc(375)] Successfully logged conversion event
[28748:28748:0829/224122.413191:VERBOSE3:conversions.cc(398)] Successfully appended conversion to queue
[28748:28748:0829/224122.423904:VERBOSE1:conversions.cc(503)] Convert campaign id 8b30cb36-e5d4-460b-9e95-3199d80720bb, creative set id 46fde2a5-3cef-4960-bd77-36af52eb3192, creative instance id e793e5b5-c073-4ceb-8174-f5462d782d95 and advertiser id 9db2f01d-07d4-409b-a017-8415c80df432 in 18 hours, 2 minutes, 37 seconds at 4:43 PM

Verified the conversion queue contains the conversion id

Verified the envelop has been attached to the confirmation