ENH: retain attrs when concat dataframes
#### Is your feature request related to a problem?

I wish the attrs could be retained when concat data frames.

```
d = {'col1': [1, 2], 'col2': [3, 4]}
df1 = pd.DataFrame(data=d)
df1.attrs = {1:1}
df2 = pd.DataFrame(data=d)
df2.attrs = {1:1}
pd.concat([df1, df2]).attrs
{}
```

#### Describe the solution you'd like

```
d = {'col1': [1, 2], 'col2': [3, 4]}
df1 = pd.DataFrame(data=d)
df1.attrs = {1:1}
df2 = pd.DataFrame(data=d)
df2.attrs = {1:1}
pd.concat([df1, df2]).attrs
{1: 1}
```

#### API breaking implications

N/A

#### Describe alternatives you've considered

N/A