feat(builds): adds build tag commands

[l2ysho]

Adds two new CLI commands for managing Actor build tags:

New Commands

apify builds add-tag - Adds a tag to a specific Actor build

USAGE
  $ apify builds add-tag -b <value> -t <value>

FLAGS
  -b, --build=<value>  The build ID to tag.
  -t, --tag=<value>    The tag to add to the build.

apify builds remove-tag - Removes a tag from a specific Actor build

USAGE
  $ apify builds remove-tag -b <value> -t <value> [-y]

FLAGS
  -b, --build=<value>  The build ID to remove the tag from.
  -t, --tag=<value>    The tag to remove from the build.
  -y, --yes            Automatic yes to prompts; assume "yes" as answer to all prompts.

Features

• Validates build exists and has SUCCEEDED status before tagging
• Shows informative message when reassigning an existing tag to a different build
• Confirmation prompt before removing a tag (can be skipped with --yes flag)
• Clear error messages for invalid operations

Example Usage

# Add a "beta" tag to a build
apify builds add-tag -b abc123 -t beta

# Remove a tag from a build
apify builds remove-tag -b abc123 -t beta --yes

Changes

• src/commands/builds/add-tag.ts - New command
• src/commands/builds/remove-tag.ts - New command
• src/commands/builds/_index.ts - Register new subcommands
• test/api/commands/builds/tags.test.ts - API tests

Closes #997

[vladfrangu]

Looks great past these small things! Also, should we consider an apify actors add-tag/remove-tag at the actor level (so smth like apify actors add-tag <actor id> <build id> <tag>?