Add additional logging to help diagnose issues when downloading catalogs

[tmancey]

Add additional logging to help diagnose issues when downloading catalogs and fetch the latest catalog every 15 minutes instead of every 2 hours if the --brave-ads-debug command-line arg is passed

[LaurenWags]

Verified passed with

Brave	0.65.97 Chromium: 74.0.3729.131 (Official Build) beta(64-bit)
Revision	518a41c1fa7ce1c8bb5e22346e82e42b4d76a96f-refs/branch-heads/3729@{#954}
OS	Mac OS X

1. Launched clean profile with --enable-logging=stderr --log-level=2 --vmodule=brave_ads=3 --brave-ads-debug.
2. Enabled Rewards.
3. Saw Start collecting activity in 962 seconds in terminal (roughly 16 minutes).
4. Verified 962 seconds later a new catalog was pulled (verified terminal messaging).
5. Verified another Start collecting activity message was displayed in the terminal again - this time for 953 seconds which is just under 16 minutes.

Verification passed on

Brave	0.65.97 Chromium: 74.0.3729.131 (Official Build) beta(64-bit)
Revision	518a41c1fa7ce1c8bb5e22346e82e42b4d76a96f-refs/branch-heads/3729@{#954}
OS	Ubuntu 18.04 LTS

Used STR provided by @LaurenWags

Verification passed on

Brave	0.65.107 Chromium: 75.0.3770.38 (Official Build) beta (64-bit)
Revision	3860105745f2b12537da9e9f048f14c3f52ba970-refs/branch-heads/3770@{#618}
OS	Windows 10 OS Version 1803 (Build 17134.523)

• Verified the above STR provided by @LaurenWags
• Verified the logs in chrome_debug.log