[Widget] Add messaging within widget when currency is below min value

[srirambv]

Description

Add messaging within widget when currency is below min value

Steps to Reproduce

1. Open Bitcoin.com widget
2. Enter a very low value like 0 or 0.50 for amount
3. Click on Buy, landing page loads and adds a default value of 200. Console logs error for value below min amount
4. In certain situation the buy modal on landing page fails to load itself

Actual result:

Default Value	No Buy screen

Expected result:

Should probably show min amount message on widget instead of loading the landing page and pre-populate with min amount

Reproduces how often:

Easy

Brave version (brave://version info)

Brave	1.17.7 Chromium: 86.0.4240.55 (Official Build) nightly (x86_64)
Revision	a6d625ef6f7fe8ea0675f1cf759155a05ee1be40-refs/branch-heads/4240@{#953}
OS	macOS Version 10.15.7 (Build 19H2)/ Linux/ Windows 10 OS Version 1809 (Build 17763.1457)

Version/Channel Information:

• Can you reproduce this issue with the current release? NA
• Can you reproduce this issue with the beta channel? NA
• Can you reproduce this issue with the nightly channel? Yes

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields? NA
• Does the issue resolve itself when disabling Brave Rewards? NA
• Is the issue reproducible on the latest version of Chrome? NA

Miscellaneous Information:

cc: @ryanml @rebron

[srirambv]

Verification passed on

Brave	1.17.61 Chromium: 86.0.4240.185 (Official Build) beta (64-Bit)
Revision	37e6f852ed18086458552039ad26421aa9fc7acc-refs/branch-heads/4240@{#1377}
OS	Linux

• Verified warning message is shown when amount entered is below min value
  

---

Verification passed on

Brave	1.17.61 Chromium: 86.0.4240.185 (Official Build) beta (64-Bit)
Revision	37e6f852ed18086458552039ad26421aa9fc7acc-refs/branch-heads/4240@{#1377}
OS	Windows 10 OS Version 1809 (Build 17763.1518)

• Verified warning message is shown when amount entered is below min value
  

---

Verification passed on

Brave	1.17.61 Chromium: 86.0.4240.185 (Official Build) beta (x86_64)
Revision	37e6f852ed18086458552039ad26421aa9fc7acc-refs/branch-heads/4240@{#1377}
OS	macOS Version 10.15.7 (Build 19H2)

• Verified warning message is shown when amount entered is below min value