BUG: when attrs lost on original dataframe, copy loses the attrs as well
- [x] I have checked that this issue has not already been reported.

- [x] I have confirmed this bug exists on the latest version of pandas.

- [x] (optional) I have confirmed this bug exists on the master branch of pandas.

---

Possibly related to:
- #28283
- #35425 

#### Code Sample, a copy-pastable example

```python
df = pandas.DataFrame({"a": [1]})
df.a.attrs = {"test": "test"}
df2 = df.copy()  # same behavior for  df.reset_index()
```
```python
df2.a.attrs
```
```
{}
```
```python
df.a.attrs
```
```
{}
```


#### Problem description

Ideally, when making a copy, the attributes will be preserved on both dataframes.

#### Expected Output

```python
df2.a.attrs
```
```
 {"test": "test"}
```
```python
df.a.attrs
```
```
 {"test": "test"}
```

#### Output of ``pd.show_versions()``

<details>


INSTALLED VERSIONS
------------------
commit           : 1963b810b3613baefe4b869bb9d034cfc9a027ef
python           : 3.7.9.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.4.0-73-generic
Version          : #82-Ubuntu SMP Wed Apr 14 17:39:42 UTC 2021
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.3.0.dev0+1660.g1963b810b3
numpy            : 1.20.1
pytz             : 2020.1
dateutil         : 2.8.1
pip              : 21.0.1
setuptools       : 49.1.0
Cython           : 0.29.23
pytest           : 6.2.2
hypothesis       : 6.13.0
sphinx           : 3.5.4
blosc            : 1.10.2
feather          : None
xlsxwriter       : 1.4.3
lxml.etree       : 4.6.2
html5lib         : 1.1
pymysql          : None
psycopg2         : 2.8.6 (dt dec pq3 ext lo64)
jinja2           : 2.11.3
IPython          : 7.20.0
pandas_datareader: None
bs4              : 4.9.3
bottleneck       : 1.3.2
fsspec           : 2021.05.0
fastparquet      : 0.6.3
gcsfs            : 2021.05.0
matplotlib       : 3.3.4
numexpr          : 2.7.3
odfpy            : None
openpyxl         : 3.0.7
pandas_gbq       : None
pyarrow          : 4.0.0
pyxlsb           : None
s3fs             : 2021.05.0
scipy            : 1.6.0
sqlalchemy       : 1.3.23
tables           : 3.6.1
tabulate         : 0.8.7
xarray           : 0.17.1.dev149+g49aa235f.d20210518
xlrd             : 2.0.1
xlwt             : 1.3.0
numba            : 0.53.1

​
</details>
