add type validation and some brief descriptions for better-comments.tags (configuration of the extension)

[Take-Me1010]

Hello, the extension better-comments is really useful and I have used it for 2 years! Thanks!!

This PR includes JSON schema and some brief descriptions for configurations of better-comments.tags.
This PR will allow users to more easily review and customize the settings of tags!

In the schema, the properties required are tag, color, and backgroundColor because these properties seem essential in the source code. If not correct, I will modify it.

[Take-Me1010]

for the property color, we can set not only #FFFFFF like style but also #FFFFFFAA or #RGB styles.
I found that in vscode theme color...

So this PR need to reflect them.

In addition, the properties color and backgroundColor seem not to be required. I will modify them in a day or so.

[Take-Me1010]

Now I modified color validation.
In addition, only tag property is made required.
Please consider merging. Thanks!