Fix the execution failure of file content appending scene

[xcaspar]

Signed-off-by: xcaspar [email protected]

Describe what this PR does / why we need it

chaosblade-io/chaosblade#636

Does this pull request fix one issue?

Describe how you did it

Solve the problem of equal sign under base64 encoding.

Describe how to verify it

Package and test it.

[root@zk003 chaosblade-1.4.0]# ./blade create file append --debug 'true' --filepath '/root/common-alarm.log' --count '2' --enable-base64 'true' --interval '1' --content 'eyJrZXl3b3JkIjoiU2FlSm9iRXJyb3IiLCJtZXNzYWdlIjoiY2hhb3MtLUt1YmVybmV0ZXNBY3JUb2tlblVwZGF0ZUpvYiNoYW5kbGVTeW5jQnlLOHNOYW1lc3BhY2UgZXhlY3V0ZSBlcnJvciwgcGxlYXNlIGNoZWNrIHlvdSBqb2IhIGVycm9yIG1lc3NhZ2UgaXMgSW52b2NhdGlvbiBmYWlsZWQuIiwidGltZSI6MTYzOTY3MDU1MTY5OX0='
{"code":200,"success":true,"result":"a31d75e1dd39a999"}

#cat /root/common-alarm.log

{"keyword":"SaeJobError","message":"chaos--KubernetesAcrTokenUpdateJob#handleSyncByK8sNamespace execute error, please check you job! error message is Invocation failed.","time":1639670551699}

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