Add config option for connection string

[nirinchev]

Adds the following connect options:

• readPreference
• readConcern
• writeConcern.w
• timeoutMS

I've tried to strike a balance between giving users control and not going overboard wtih config options that may never get used.

Additionally, refactored the env variable parsing where instead of using the defaults to look up env variables, we now construct an object from all env variables that start with MDB_MCP_.

[Copilot]

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (2)

src/tools/mongodb/connect.ts:75

• Verify that wrapping config.connectOptions.writeConcern inside an object with the key 'w' matches the expected structure for NodeDriverServiceProvider.connect. If a different structure is required, adjust accordingly.

w: config.connectOptions.writeConcern,

src/config.ts:124

• [nitpick] The function name 'SNAKE_CASE_toCamelCase' mixes naming conventions. Consider renaming it to 'snakeToCamelCase' for consistency.

return str.toLowerCase().replace(/([-_][a-z])/g, (group) => group.toUpperCase().replace('_', ''));