Monthly Dropdown should not be available in Panel until Monthly donation is made.

[ryanml]

Description

The dropdown to select a recurring contribution in the Rewards Panel should not be visible until a user has made an ad-hoc donation, selecting "Make this Monthly" for that publisher.

Test plan:

1. Start Brave, enable Rewards.
2. Go to a verified publisher's site.
3. Open the Rewards Panel, ensure that no dropdown is available.
4. Send them a recurring tip.
5. Re-open the panel and confirm the dropdown is present with the current recurring amount.
6. Change the donation amount via the panel to 0.0
7. Confirm the dropdown is no longer available.

[GeetaSarvadnya]

Verification passed on

Brave	0.65.93 Chromium: 74.0.3729.131 (Official Build) beta (64-bit)
Revision	518a41c1fa7ce1c8bb5e22346e82e42b4d76a96f-refs/branch-heads/3729@{#954}
OS	Windows 10 OS Build 17134.523

• Verified the test plan from Adds functionality to monthly contribution dropdown (Panel, #3 origin) brave-core#2069

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

• Verified the test plan from Adds functionality to monthly contribution dropdown (Panel, #3 origin) brave-core#2069
• Logged Monthly tip value is not trimmed in Rewards Panel #4502

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

• Verified the test plan from Adds functionality to monthly contribution dropdown (Panel, #3 origin) brave-core#2069
• Encountered Monthly tip value is not trimmed in Rewards Panel #4502
• Logged BAT is sometimes truncated on panel for 'Tip this site monthly' value #4503, recurring tip amount change not immediately reflected on external monitor #4505, Monthly tip dropdown on panel allows for tipping more than wallet balance #4506