TIP-93 part 3: give Treasury committee discretion to adjust tBTC fees

Following extensive deliberation by Threshold Treasury committee and then the community (see Forum discussion in link below), this is the 3rd of 4 snapshots that cover the facets to be decided (mint fee, redeem fee, Treasury committee authorization, 30-day delay for fee changes), while avoiding inevitable "split votes" by trying to combine them.

Per Forum discussion, some tokenholders favor authorizing the elected Treasury committee discretion to adjust tBTC mint and/or redeem fees. The stated rationale in TIP-75 tBTC Bridge fee holiday part 2 was: "Moreover, in an effort to ensure a faster reaction time and greater flexibility in adapting to rapidly changing market conditions, we propose that the Treasury Guild be granted the authority for six (6) months to direct the Threshold Council to adjust fee parameters. By delegating this decision to the Treasury Guild Committee it will allow for a more agile and responsive adjustment of fees in line with market fluctuations."

In order to provide a range of options should tokenholders vote here to approve some form of committee discretion, while avoiding malformed choices leading to split votes, this vote addresses the basic question first. If approved, another vote will follow after Forum alignment on options.