Consistent -c / -C for configuration file option

[morgo]

Minor issue:

tikv-importer uses a capital -C for the config file option versus tidb-lightning that uses a lower case -c. Is it possible to make these consistent?

Additional research:

• tidb: does not have single letter flag (-config)
• tikv: uses capital -C
• pd: does not have a single letter flag (-config)

[kennytm]

(Also tracked in Jira as TOOL-363.)

Further information for our other tools

Project	Binary	Flag
tidb-binlog	drainer	-config (-c means "parallel worker count")
tidb-binlog	pump	-config
tidb-enterprise-tools	syncer	-config
tidb-enterprise-tools	loader	-config

I think we must add -config in additional to -c. But I don't think we should remove -c or change it to -C as this will unnecessarily break backward compatibility.

[morgo]

In unreleased tools, it is okay to break backwards compatibility (why I bring it up now :-)).

But in released tools: yes, best not to change.

[kennytm]

Unfortunately the tool has given to several customers already so it's not completely unreleased 😂.

[morgo]

OK :-) My mistake.