Feat: Add My Near Wallet to Selector

[gutsyphilip]

Description

Since we are migrating the NEAR Wallet to the My Near Wallet domain(mynearwallet.com), we need to add a new option to the selector for the new wallet.

The goal is to eventually deprecate the Near wallet domain(wallet.near.org) once migration is completed.

Closes # (issue)

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

Type of change. This type of change is the main reason for the PR.

• FIX - a PR of this type patches a bug.
• FEATURE - a PR of this type introduces a new feature.
• BUILD - a PR of this type introduces build changes.
• CI - a PR of this type introduces CI changes.
• DOCS - a PR of this type introduces DOCS improvement.
• STYLE - a PR of this type introduces style changes.
• REFACTOR - a PR of this type introduces refactoring.
• PERFORMANCE - a PR of this type introduces performance changes.
• TEST - a PR of this type adds more tests.
• CHORE - a PR introduces other changes than the specified above.

Breaking changes

• BREAKING CHANGE - SPECIFY: _______
• NO BREAKING CHANGE - this PR doesn't contain any breaking changes and it's backwards compatible

[lewis-sqa]

Hey @gutsyphilip, thanks for raising this PR!

We're in the process of releasing a new major version (currently on the dev branch) of the library that means the structure of a wallet has changed quite significantly. Since this new version is only a matter of days away, we would prefer if the changes were made against dev.

I've raised a POC variation of your work here that wraps the existing NEAR Wallet implementation to reduce code duplication as it appears My NEAR Wallet functions 1:1 with NEAR Wallet with only the walletUrl that changes?

I noticed My NEAR Wallet lacks a betanet variation but includes a staging environment. To avoid confusion, I've omitted this link and forced the dApp developer to explicitly define the walletUrl for networks that aren't mainnet or testnet.