Partners: secondary hashtag field size is too small in the DB

[emi420]

Describe the bug
The limit for the secondary hashtag column is 50 characters, which is too small.

To Reproduce

1. Go to create a partner
2. Try with several hashtags (+50 characters) in the secondary hashtag field
3. Click "Save"
4. It will fail because the API returns Error 500

Expected behavior

To accept more than 50 characters for the secondary hashtag.

Additional info

Check this migration file:

https://github.com/hotosm/tasking-manager/blob/develop/migrations/versions/e8ffa33a9c18_.py#L26C1-L26C23

[ramyaragupathy]

cc @manjitapandey @prabinoid @kaditya97