Among all the characters that are allowed in a URL, both the percentage
sign "%" and the single quotation mark "'" needs escaping when written
as a environment variable in a systemd service file. While the single
quotation mark may be rare, the percentage sign is widely used to escape
characters in a URL. This is especially common in proxy setting, where
username and password may contain special characters that need
percentage escaping. This patch applies the following replacements:
% -> %%
' -> \'