cmd/geth: standardize the action of importing bls account

[buddh0]

Description

cmd/geth: standardize the action of importing bls account

Rationale

there are 3 issues when using geth bls account

1. no trim '\r\n' when read password from file.
   when use vim or echo command to write password into a file, a '\r' or '\n' will be added automaticly
   this PR will do the trim by following geth account

2. some related flags have not set field Category, so they will not be displayed in help info
   this PR fix it

3. putting a bls private key into wallet viewed as a new action
   only putting a keystore file into wallet will be viewed as a import action
   but geth account can put a private key into wallet by a import action
   and others, in metamask, the import action both accept a file including a private key or a keystore file

   so in this PR, putting a bls private key into wallet will be viewed as a import action instead of a new action.

4. when new a bls account, use the bls wallet password to encrypt it into a keystore file
   so no need a blsaccountpassword any more, bring much convenient

5. when import a bls account with a keystore file, rename blsaccountpassword to importedaccountpassword,
   to reduce ambiguity.

to demostrate the usage of geth bls account, a shell is provided,
and using it to test these above features is easily

Example

run bash bls-account-usage-demo.sh in bsc/cmd/geth/testdata

Changes

Notable changes:

• add each change in a bullet point here
• ...

[keefel]

LGTM